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