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