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
22using namespace clang;
23
24using Cl = Expr::Classification;
25
26static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E);
27static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D);
28static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T);
29static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E);
30static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E);
31static Cl::Kinds ClassifyConditional(ASTContext &Ctx,
32 const Expr *trueExpr,
33 const Expr *falseExpr);
34static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
35 Cl::Kinds Kind, SourceLocation &Loc);
36
37Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {
38 assert(!TR->isReferenceType() && "Expressions can't have reference type.");
39
40 Cl::Kinds kind = ClassifyInternal(Ctx, E: 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, E: this, Kind: kind, Loc&: *Loc);
79 return Classification(kind, modifiable);
80}
81
82/// Classify an expression which creates a temporary, based on its type.
83static 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
94static 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(T: 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
108static 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 // 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 case Expr::CXXUuidofExprClass:
128 // Unresolved lookups and uncorrected typos 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::TypoExprClass:
133 case Expr::DependentCoawaitExprClass:
134 case Expr::CXXDependentScopeMemberExprClass:
135 case Expr::DependentScopeDeclRefExprClass:
136 // ObjC instance variables are lvalues
137 // FIXME: ObjC++0x might have different rules
138 case Expr::ObjCIvarRefExprClass:
139 case Expr::FunctionParmPackExprClass:
140 case Expr::MSPropertyRefExprClass:
141 case Expr::MSPropertySubscriptExprClass:
142 case Expr::ArraySectionExprClass:
143 case Expr::OMPArrayShapingExprClass:
144 case Expr::OMPIteratorExprClass:
145 case Expr::HLSLOutArgExprClass:
146 return Cl::CL_LValue;
147
148 // C++ [expr.prim.general]p1: A string literal is an lvalue.
149 case Expr::StringLiteralClass:
150 // @encode is equivalent to its string
151 case Expr::ObjCEncodeExprClass:
152 // Except we special case them as prvalues when they are used to
153 // initialize a char array.
154 return E->isLValue() ? Cl::CL_LValue : Cl::CL_PRValue;
155
156 // __func__ and friends are too.
157 // The char array initialization special case also applies
158 // when they are transparent.
159 case Expr::PredefinedExprClass: {
160 auto *PE = cast<PredefinedExpr>(E);
161 const StringLiteral *SL = PE->getFunctionName();
162 if (PE->isTransparent())
163 return SL ? ClassifyInternal(Ctx, SL) : Cl::CL_LValue;
164 assert(!SL || SL->isLValue());
165 return Cl::CL_LValue;
166 }
167
168 // C99 6.5.2.5p5 says that compound literals are lvalues.
169 // In C++, they're prvalue temporaries, except for file-scope arrays.
170 case Expr::CompoundLiteralExprClass:
171 return !E->isLValue() ? ClassifyTemporary(T: E->getType()) : Cl::CL_LValue;
172
173 // Expressions that are prvalues.
174 case Expr::CXXBoolLiteralExprClass:
175 case Expr::CXXPseudoDestructorExprClass:
176 case Expr::UnaryExprOrTypeTraitExprClass:
177 case Expr::CXXNewExprClass:
178 case Expr::CXXNullPtrLiteralExprClass:
179 case Expr::ImaginaryLiteralClass:
180 case Expr::GNUNullExprClass:
181 case Expr::OffsetOfExprClass:
182 case Expr::CXXThrowExprClass:
183 case Expr::ShuffleVectorExprClass:
184 case Expr::ConvertVectorExprClass:
185 case Expr::IntegerLiteralClass:
186 case Expr::FixedPointLiteralClass:
187 case Expr::CharacterLiteralClass:
188 case Expr::AddrLabelExprClass:
189 case Expr::CXXDeleteExprClass:
190 case Expr::ImplicitValueInitExprClass:
191 case Expr::BlockExprClass:
192 case Expr::FloatingLiteralClass:
193 case Expr::CXXNoexceptExprClass:
194 case Expr::CXXScalarValueInitExprClass:
195 case Expr::TypeTraitExprClass:
196 case Expr::ArrayTypeTraitExprClass:
197 case Expr::ExpressionTraitExprClass:
198 case Expr::ObjCSelectorExprClass:
199 case Expr::ObjCProtocolExprClass:
200 case Expr::ObjCStringLiteralClass:
201 case Expr::ObjCBoxedExprClass:
202 case Expr::ObjCArrayLiteralClass:
203 case Expr::ObjCDictionaryLiteralClass:
204 case Expr::ObjCBoolLiteralExprClass:
205 case Expr::ObjCAvailabilityCheckExprClass:
206 case Expr::ParenListExprClass:
207 case Expr::SizeOfPackExprClass:
208 case Expr::SubstNonTypeTemplateParmPackExprClass:
209 case Expr::AsTypeExprClass:
210 case Expr::ObjCIndirectCopyRestoreExprClass:
211 case Expr::AtomicExprClass:
212 case Expr::CXXFoldExprClass:
213 case Expr::ArrayInitLoopExprClass:
214 case Expr::ArrayInitIndexExprClass:
215 case Expr::NoInitExprClass:
216 case Expr::DesignatedInitUpdateExprClass:
217 case Expr::SourceLocExprClass:
218 case Expr::ConceptSpecializationExprClass:
219 case Expr::RequiresExprClass:
220 return Cl::CL_PRValue;
221
222 case Expr::EmbedExprClass:
223 // Nominally, this just goes through as a PRValue until we actually expand
224 // it and check it.
225 return Cl::CL_PRValue;
226
227 // Make HLSL this reference-like
228 case Expr::CXXThisExprClass:
229 return Lang.HLSL ? Cl::CL_LValue : Cl::CL_PRValue;
230
231 case Expr::ConstantExprClass:
232 return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr());
233
234 // Next come the complicated cases.
235 case Expr::SubstNonTypeTemplateParmExprClass:
236 return ClassifyInternal(Ctx,
237 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
238
239 case Expr::PackIndexingExprClass: {
240 // A pack-index-expression always expands to an id-expression.
241 // Consider it as an LValue expression.
242 if (cast<PackIndexingExpr>(E)->isInstantiationDependent())
243 return Cl::CL_LValue;
244 return ClassifyInternal(Ctx, cast<PackIndexingExpr>(E)->getSelectedExpr());
245 }
246
247 // C, C++98 [expr.sub]p1: The result is an lvalue of type "T".
248 // C++11 (DR1213): in the case of an array operand, the result is an lvalue
249 // if that operand is an lvalue and an xvalue otherwise.
250 // Subscripting vector types is more like member access.
251 case Expr::ArraySubscriptExprClass:
252 if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
253 return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
254 if (Lang.CPlusPlus11) {
255 // Step over the array-to-pointer decay if present, but not over the
256 // temporary materialization.
257 auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts();
258 if (Base->getType()->isArrayType())
259 return ClassifyInternal(Ctx, Base);
260 }
261 return Cl::CL_LValue;
262
263 // Subscripting matrix types behaves like member accesses.
264 case Expr::MatrixSubscriptExprClass:
265 return ClassifyInternal(Ctx, cast<MatrixSubscriptExpr>(E)->getBase());
266
267 // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
268 // function or variable and a prvalue otherwise.
269 case Expr::DeclRefExprClass:
270 if (E->getType() == Ctx.UnknownAnyTy)
271 return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
272 ? Cl::CL_PRValue : Cl::CL_LValue;
273 return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
274
275 // Member access is complex.
276 case Expr::MemberExprClass:
277 return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
278
279 case Expr::UnaryOperatorClass:
280 switch (cast<UnaryOperator>(E)->getOpcode()) {
281 // C++ [expr.unary.op]p1: The unary * operator performs indirection:
282 // [...] the result is an lvalue referring to the object or function
283 // to which the expression points.
284 case UO_Deref:
285 return Cl::CL_LValue;
286
287 // GNU extensions, simply look through them.
288 case UO_Extension:
289 return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
290
291 // Treat _Real and _Imag basically as if they were member
292 // expressions: l-value only if the operand is a true l-value.
293 case UO_Real:
294 case UO_Imag: {
295 const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
296 Cl::Kinds K = ClassifyInternal(Ctx, E: Op);
297 if (K != Cl::CL_LValue) return K;
298
299 if (isa<ObjCPropertyRefExpr>(Op))
300 return Cl::CL_SubObjCPropertySetting;
301 return Cl::CL_LValue;
302 }
303
304 // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
305 // lvalue, [...]
306 // Not so in C.
307 case UO_PreInc:
308 case UO_PreDec:
309 return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
310
311 default:
312 return Cl::CL_PRValue;
313 }
314
315 case Expr::RecoveryExprClass:
316 case Expr::OpaqueValueExprClass:
317 return ClassifyExprValueKind(Lang, E, Kind: E->getValueKind());
318
319 // Pseudo-object expressions can produce l-values with reference magic.
320 case Expr::PseudoObjectExprClass:
321 return ClassifyExprValueKind(Lang, E,
322 cast<PseudoObjectExpr>(E)->getValueKind());
323
324 // Implicit casts are lvalues if they're lvalue casts. Other than that, we
325 // only specifically record class temporaries.
326 case Expr::ImplicitCastExprClass:
327 return ClassifyExprValueKind(Lang, E, Kind: E->getValueKind());
328
329 // C++ [expr.prim.general]p4: The presence of parentheses does not affect
330 // whether the expression is an lvalue.
331 case Expr::ParenExprClass:
332 return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
333
334 // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
335 // or a void expression if its result expression is, respectively, an
336 // lvalue, a function designator, or a void expression.
337 case Expr::GenericSelectionExprClass:
338 if (cast<GenericSelectionExpr>(E)->isResultDependent())
339 return Cl::CL_PRValue;
340 return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
341
342 case Expr::BinaryOperatorClass:
343 case Expr::CompoundAssignOperatorClass:
344 // C doesn't have any binary expressions that are lvalues.
345 if (Lang.CPlusPlus)
346 return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
347 return Cl::CL_PRValue;
348
349 case Expr::CallExprClass:
350 case Expr::CXXOperatorCallExprClass:
351 case Expr::CXXMemberCallExprClass:
352 case Expr::UserDefinedLiteralClass:
353 case Expr::CUDAKernelCallExprClass:
354 return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
355
356 case Expr::CXXRewrittenBinaryOperatorClass:
357 return ClassifyInternal(
358 Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm());
359
360 // __builtin_choose_expr is equivalent to the chosen expression.
361 case Expr::ChooseExprClass:
362 return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
363
364 // Extended vector element access is an lvalue unless there are duplicates
365 // in the shuffle expression.
366 case Expr::ExtVectorElementExprClass:
367 if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
368 return Cl::CL_DuplicateVectorComponents;
369 if (cast<ExtVectorElementExpr>(E)->isArrow())
370 return Cl::CL_LValue;
371 return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
372
373 // Simply look at the actual default argument.
374 case Expr::CXXDefaultArgExprClass:
375 return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
376
377 // Same idea for default initializers.
378 case Expr::CXXDefaultInitExprClass:
379 return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
380
381 // Same idea for temporary binding.
382 case Expr::CXXBindTemporaryExprClass:
383 return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
384
385 // And the cleanups guard.
386 case Expr::ExprWithCleanupsClass:
387 return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
388
389 // Casts depend completely on the target type. All casts work the same.
390 case Expr::CStyleCastExprClass:
391 case Expr::CXXFunctionalCastExprClass:
392 case Expr::CXXStaticCastExprClass:
393 case Expr::CXXDynamicCastExprClass:
394 case Expr::CXXReinterpretCastExprClass:
395 case Expr::CXXConstCastExprClass:
396 case Expr::CXXAddrspaceCastExprClass:
397 case Expr::ObjCBridgedCastExprClass:
398 case Expr::BuiltinBitCastExprClass:
399 // Only in C++ can casts be interesting at all.
400 if (!Lang.CPlusPlus) return Cl::CL_PRValue;
401 return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
402
403 case Expr::CXXUnresolvedConstructExprClass:
404 return ClassifyUnnamed(Ctx,
405 cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
406
407 case Expr::BinaryConditionalOperatorClass: {
408 if (!Lang.CPlusPlus) return Cl::CL_PRValue;
409 const auto *co = cast<BinaryConditionalOperator>(E);
410 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
411 }
412
413 case Expr::ConditionalOperatorClass: {
414 // Once again, only C++ is interesting.
415 if (!Lang.CPlusPlus) return Cl::CL_PRValue;
416 const auto *co = cast<ConditionalOperator>(E);
417 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
418 }
419
420 // ObjC message sends are effectively function calls, if the target function
421 // is known.
422 case Expr::ObjCMessageExprClass:
423 if (const ObjCMethodDecl *Method =
424 cast<ObjCMessageExpr>(E)->getMethodDecl()) {
425 Cl::Kinds kind = ClassifyUnnamed(Ctx, T: Method->getReturnType());
426 return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
427 }
428 return Cl::CL_PRValue;
429
430 // Some C++ expressions are always class temporaries.
431 case Expr::CXXConstructExprClass:
432 case Expr::CXXInheritedCtorInitExprClass:
433 case Expr::CXXTemporaryObjectExprClass:
434 case Expr::LambdaExprClass:
435 case Expr::CXXStdInitializerListExprClass:
436 return Cl::CL_ClassTemporary;
437
438 case Expr::VAArgExprClass:
439 return ClassifyUnnamed(Ctx, T: E->getType());
440
441 case Expr::DesignatedInitExprClass:
442 return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
443
444 case Expr::StmtExprClass: {
445 const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
446 if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
447 return ClassifyUnnamed(Ctx, LastExpr->getType());
448 return Cl::CL_PRValue;
449 }
450
451 case Expr::PackExpansionExprClass:
452 return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
453
454 case Expr::MaterializeTemporaryExprClass:
455 return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
456 ? Cl::CL_LValue
457 : Cl::CL_XValue;
458
459 case Expr::InitListExprClass:
460 // An init list can be an lvalue if it is bound to a reference and
461 // contains only one element. In that case, we look at that element
462 // for an exact classification. Init list creation takes care of the
463 // value kind for us, so we only need to fine-tune.
464 if (E->isPRValue())
465 return ClassifyExprValueKind(Lang, E, Kind: E->getValueKind());
466 assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
467 "Only 1-element init lists can be glvalues.");
468 return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
469
470 case Expr::CoawaitExprClass:
471 case Expr::CoyieldExprClass:
472 return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr());
473 case Expr::SYCLUniqueStableNameExprClass:
474 case Expr::OpenACCAsteriskSizeExprClass:
475 return Cl::CL_PRValue;
476 break;
477
478 case Expr::CXXParenListInitExprClass:
479 if (isa<ArrayType>(E->getType()))
480 return Cl::CL_ArrayTemporary;
481 return Cl::CL_ClassTemporary;
482 }
483
484 llvm_unreachable("unhandled expression kind in classification");
485}
486
487/// ClassifyDecl - Return the classification of an expression referencing the
488/// given declaration.
489static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
490 // C++ [expr.prim.id.unqual]p3: The result is an lvalue if the entity is a
491 // function, variable, or data member, or a template parameter object and a
492 // prvalue otherwise.
493 // In C, functions are not lvalues.
494 // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
495 // lvalue unless it's a reference type or a class type (C++ [temp.param]p8),
496 // so we need to special-case this.
497
498 if (const auto *M = dyn_cast<CXXMethodDecl>(Val: D)) {
499 if (M->isImplicitObjectMemberFunction())
500 return Cl::CL_MemberFunction;
501 if (M->isStatic())
502 return Cl::CL_LValue;
503 return Cl::CL_PRValue;
504 }
505
506 bool islvalue;
507 if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(Val: D))
508 islvalue = NTTParm->getType()->isReferenceType() ||
509 NTTParm->getType()->isRecordType();
510 else
511 islvalue =
512 isa<VarDecl, FieldDecl, IndirectFieldDecl, BindingDecl, MSGuidDecl,
513 UnnamedGlobalConstantDecl, TemplateParamObjectDecl>(Val: D) ||
514 (Ctx.getLangOpts().CPlusPlus &&
515 (isa<FunctionDecl, MSPropertyDecl, FunctionTemplateDecl>(Val: D)));
516
517 return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
518}
519
520/// ClassifyUnnamed - Return the classification of an expression yielding an
521/// unnamed value of the given type. This applies in particular to function
522/// calls and casts.
523static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
524 // In C, function calls are always rvalues.
525 if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
526
527 // C++ [expr.call]p10: A function call is an lvalue if the result type is an
528 // lvalue reference type or an rvalue reference to function type, an xvalue
529 // if the result type is an rvalue reference to object type, and a prvalue
530 // otherwise.
531 if (T->isLValueReferenceType())
532 return Cl::CL_LValue;
533 const auto *RV = T->getAs<RValueReferenceType>();
534 if (!RV) // Could still be a class temporary, though.
535 return ClassifyTemporary(T);
536
537 return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
538}
539
540static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
541 if (E->getType() == Ctx.UnknownAnyTy)
542 return (isa<FunctionDecl>(Val: E->getMemberDecl())
543 ? Cl::CL_PRValue : Cl::CL_LValue);
544
545 // Handle C first, it's easier.
546 if (!Ctx.getLangOpts().CPlusPlus) {
547 // C99 6.5.2.3p3
548 // For dot access, the expression is an lvalue if the first part is. For
549 // arrow access, it always is an lvalue.
550 if (E->isArrow())
551 return Cl::CL_LValue;
552 // ObjC property accesses are not lvalues, but get special treatment.
553 Expr *Base = E->getBase()->IgnoreParens();
554 if (isa<ObjCPropertyRefExpr>(Val: Base))
555 return Cl::CL_SubObjCPropertySetting;
556 return ClassifyInternal(Ctx, E: Base);
557 }
558
559 NamedDecl *Member = E->getMemberDecl();
560 // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
561 // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
562 // E1.E2 is an lvalue.
563 if (const auto *Value = dyn_cast<ValueDecl>(Member))
564 if (Value->getType()->isReferenceType())
565 return Cl::CL_LValue;
566
567 // Otherwise, one of the following rules applies.
568 // -- If E2 is a static member [...] then E1.E2 is an lvalue.
569 if (isa<VarDecl>(Val: Member) && Member->getDeclContext()->isRecord())
570 return Cl::CL_LValue;
571
572 // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
573 // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
574 // otherwise, it is a prvalue.
575 if (isa<FieldDecl>(Val: Member)) {
576 // *E1 is an lvalue
577 if (E->isArrow())
578 return Cl::CL_LValue;
579 Expr *Base = E->getBase()->IgnoreParenImpCasts();
580 if (isa<ObjCPropertyRefExpr>(Val: Base))
581 return Cl::CL_SubObjCPropertySetting;
582 return ClassifyInternal(Ctx, E: E->getBase());
583 }
584
585 // -- If E2 is a [...] member function, [...]
586 // -- If it refers to a static member function [...], then E1.E2 is an
587 // lvalue; [...]
588 // -- Otherwise [...] E1.E2 is a prvalue.
589 if (const auto *Method = dyn_cast<CXXMethodDecl>(Member)) {
590 if (Method->isStatic())
591 return Cl::CL_LValue;
592 if (Method->isImplicitObjectMemberFunction())
593 return Cl::CL_MemberFunction;
594 return Cl::CL_PRValue;
595 }
596
597 // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
598 // So is everything else we haven't handled yet.
599 return Cl::CL_PRValue;
600}
601
602static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {
603 assert(Ctx.getLangOpts().CPlusPlus &&
604 "This is only relevant for C++.");
605 // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
606 // Except we override this for writes to ObjC properties.
607 if (E->isAssignmentOp())
608 return (E->getLHS()->getObjectKind() == OK_ObjCProperty
609 ? Cl::CL_PRValue : Cl::CL_LValue);
610
611 // C++ [expr.comma]p1: the result is of the same value category as its right
612 // operand, [...].
613 if (E->getOpcode() == BO_Comma)
614 return ClassifyInternal(Ctx, E: E->getRHS());
615
616 // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
617 // is a pointer to a data member is of the same value category as its first
618 // operand.
619 if (E->getOpcode() == BO_PtrMemD)
620 return (E->getType()->isFunctionType() ||
621 E->hasPlaceholderType(BuiltinType::BoundMember))
622 ? Cl::CL_MemberFunction
623 : ClassifyInternal(Ctx, E: E->getLHS());
624
625 // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
626 // second operand is a pointer to data member and a prvalue otherwise.
627 if (E->getOpcode() == BO_PtrMemI)
628 return (E->getType()->isFunctionType() ||
629 E->hasPlaceholderType(BuiltinType::BoundMember))
630 ? Cl::CL_MemberFunction
631 : Cl::CL_LValue;
632
633 // All other binary operations are prvalues.
634 return Cl::CL_PRValue;
635}
636
637static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
638 const Expr *False) {
639 assert(Ctx.getLangOpts().CPlusPlus &&
640 "This is only relevant for C++.");
641
642 // C++ [expr.cond]p2
643 // If either the second or the third operand has type (cv) void,
644 // one of the following shall hold:
645 if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
646 // The second or the third operand (but not both) is a (possibly
647 // parenthesized) throw-expression; the result is of the [...] value
648 // category of the other.
649 bool TrueIsThrow = isa<CXXThrowExpr>(Val: True->IgnoreParenImpCasts());
650 bool FalseIsThrow = isa<CXXThrowExpr>(Val: False->IgnoreParenImpCasts());
651 if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
652 : (FalseIsThrow ? True : nullptr))
653 return ClassifyInternal(Ctx, E: NonThrow);
654
655 // [Otherwise] the result [...] is a prvalue.
656 return Cl::CL_PRValue;
657 }
658
659 // Note that at this point, we have already performed all conversions
660 // according to [expr.cond]p3.
661 // C++ [expr.cond]p4: If the second and third operands are glvalues of the
662 // same value category [...], the result is of that [...] value category.
663 // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
664 Cl::Kinds LCl = ClassifyInternal(Ctx, E: True),
665 RCl = ClassifyInternal(Ctx, E: False);
666 return LCl == RCl ? LCl : Cl::CL_PRValue;
667}
668
669static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
670 Cl::Kinds Kind, SourceLocation &Loc) {
671 // As a general rule, we only care about lvalues. But there are some rvalues
672 // for which we want to generate special results.
673 if (Kind == Cl::CL_PRValue) {
674 // For the sake of better diagnostics, we want to specifically recognize
675 // use of the GCC cast-as-lvalue extension.
676 if (const auto *CE = dyn_cast<ExplicitCastExpr>(Val: E->IgnoreParens())) {
677 if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
678 Loc = CE->getExprLoc();
679 return Cl::CM_LValueCast;
680 }
681 }
682 }
683 if (Kind != Cl::CL_LValue)
684 return Cl::CM_RValue;
685
686 // This is the lvalue case.
687 // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
688 if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
689 return Cl::CM_Function;
690
691 // Assignment to a property in ObjC is an implicit setter access. But a
692 // setter might not exist.
693 if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(Val: E)) {
694 if (Expr->isImplicitProperty() &&
695 Expr->getImplicitPropertySetter() == nullptr)
696 return Cl::CM_NoSetterProperty;
697 }
698
699 CanQualType CT = Ctx.getCanonicalType(T: E->getType());
700 // Const stuff is obviously not modifiable.
701 if (CT.isConstQualified())
702 return Cl::CM_ConstQualified;
703 if (Ctx.getLangOpts().OpenCL &&
704 CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant)
705 return Cl::CM_ConstAddrSpace;
706
707 // Arrays are not modifiable, only their elements are.
708 if (CT->isArrayType() &&
709 !(Ctx.getLangOpts().HLSL && CT->isConstantArrayType()))
710 return Cl::CM_ArrayType;
711 // Incomplete types are not modifiable.
712 if (CT->isIncompleteType())
713 return Cl::CM_IncompleteType;
714
715 // Records with any const fields (recursively) are not modifiable.
716 if (const RecordType *R = CT->getAs<RecordType>())
717 if (R->hasConstFields())
718 return Cl::CM_ConstQualifiedField;
719
720 return Cl::CM_Modifiable;
721}
722
723Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
724 Classification VC = Classify(Ctx);
725 switch (VC.getKind()) {
726 case Cl::CL_LValue: return LV_Valid;
727 case Cl::CL_XValue: return LV_InvalidExpression;
728 case Cl::CL_Function: return LV_NotObjectType;
729 case Cl::CL_Void: return LV_InvalidExpression;
730 case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;
731 case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;
732 case Cl::CL_MemberFunction: return LV_MemberFunction;
733 case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
734 case Cl::CL_ClassTemporary: return LV_ClassTemporary;
735 case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
736 case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
737 case Cl::CL_PRValue: return LV_InvalidExpression;
738 }
739 llvm_unreachable("Unhandled kind");
740}
741
742Expr::isModifiableLvalueResult
743Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
744 SourceLocation dummy;
745 Classification VC = ClassifyModifiable(Ctx, Loc&: Loc ? *Loc : dummy);
746 switch (VC.getKind()) {
747 case Cl::CL_LValue: break;
748 case Cl::CL_XValue: return MLV_InvalidExpression;
749 case Cl::CL_Function: return MLV_NotObjectType;
750 case Cl::CL_Void: return MLV_InvalidExpression;
751 case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;
752 case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;
753 case Cl::CL_MemberFunction: return MLV_MemberFunction;
754 case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
755 case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
756 case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
757 case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
758 case Cl::CL_PRValue:
759 return VC.getModifiable() == Cl::CM_LValueCast ?
760 MLV_LValueCast : MLV_InvalidExpression;
761 }
762 assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
763 switch (VC.getModifiable()) {
764 case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
765 case Cl::CM_Modifiable: return MLV_Valid;
766 case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
767 case Cl::CM_Function: return MLV_NotObjectType;
768 case Cl::CM_LValueCast:
769 llvm_unreachable("CM_LValueCast and CL_LValue don't match");
770 case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
771 case Cl::CM_ConstQualified: return MLV_ConstQualified;
772 case Cl::CM_ConstQualifiedField: return MLV_ConstQualifiedField;
773 case Cl::CM_ConstAddrSpace: return MLV_ConstAddrSpace;
774 case Cl::CM_ArrayType: return MLV_ArrayType;
775 case Cl::CM_IncompleteType: return MLV_IncompleteType;
776 }
777 llvm_unreachable("Unhandled modifiable type");
778}
779

source code of clang/lib/AST/ExprClassification.cpp