clang  10.0.0svn
ExprClassification.cpp
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1 //===- ExprClassification.cpp - Expression AST Node Implementation --------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements Expr::classify.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "clang/AST/Expr.h"
14 #include "clang/AST/ASTContext.h"
15 #include "clang/AST/DeclCXX.h"
16 #include "clang/AST/DeclObjC.h"
17 #include "clang/AST/DeclTemplate.h"
18 #include "clang/AST/ExprCXX.h"
19 #include "clang/AST/ExprObjC.h"
20 #include "llvm/Support/ErrorHandling.h"
21 
22 using namespace clang;
23 
25 
26 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E);
27 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D);
29 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E);
32  const Expr *trueExpr,
33  const Expr *falseExpr);
34 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
36 
37 Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {
38  assert(!TR->isReferenceType() && "Expressions can't have reference type.");
39 
40  Cl::Kinds kind = ClassifyInternal(Ctx, this);
41  // C99 6.3.2.1: An lvalue is an expression with an object type or an
42  // incomplete type other than void.
43  if (!Ctx.getLangOpts().CPlusPlus) {
44  // Thus, no functions.
45  if (TR->isFunctionType() || TR == Ctx.OverloadTy)
46  kind = Cl::CL_Function;
47  // No void either, but qualified void is OK because it is "other than void".
48  // Void "lvalues" are classified as addressable void values, which are void
49  // expressions whose address can be taken.
50  else if (TR->isVoidType() && !TR.hasQualifiers())
52  }
53 
54  // Enable this assertion for testing.
55  switch (kind) {
56  case Cl::CL_LValue: assert(getValueKind() == VK_LValue); break;
57  case Cl::CL_XValue: assert(getValueKind() == VK_XValue); break;
58  case Cl::CL_Function:
59  case Cl::CL_Void:
67  case Cl::CL_PRValue: assert(getValueKind() == VK_RValue); break;
68  }
69 
71  if (Loc)
72  modifiable = IsModifiable(Ctx, this, kind, *Loc);
73  return Classification(kind, modifiable);
74 }
75 
76 /// Classify an expression which creates a temporary, based on its type.
78  if (T->isRecordType())
79  return Cl::CL_ClassTemporary;
80  if (T->isArrayType())
81  return Cl::CL_ArrayTemporary;
82 
83  // No special classification: these don't behave differently from normal
84  // prvalues.
85  return Cl::CL_PRValue;
86 }
87 
89  const Expr *E,
91  switch (Kind) {
92  case VK_RValue:
93  return Lang.CPlusPlus ? ClassifyTemporary(E->getType()) : Cl::CL_PRValue;
94  case VK_LValue:
95  return Cl::CL_LValue;
96  case VK_XValue:
97  return Cl::CL_XValue;
98  }
99  llvm_unreachable("Invalid value category of implicit cast.");
100 }
101 
102 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
103  // This function takes the first stab at classifying expressions.
104  const LangOptions &Lang = Ctx.getLangOpts();
105 
106  switch (E->getStmtClass()) {
107  case Stmt::NoStmtClass:
108 #define ABSTRACT_STMT(Kind)
109 #define STMT(Kind, Base) case Expr::Kind##Class:
110 #define EXPR(Kind, Base)
111 #include "clang/AST/StmtNodes.inc"
112  llvm_unreachable("cannot classify a statement");
113 
114  // First come the expressions that are always lvalues, unconditionally.
115  case Expr::ObjCIsaExprClass:
116  // C++ [expr.prim.general]p1: A string literal is an lvalue.
117  case Expr::StringLiteralClass:
118  // @encode is equivalent to its string
119  case Expr::ObjCEncodeExprClass:
120  // __func__ and friends are too.
121  case Expr::PredefinedExprClass:
122  // Property references are lvalues
123  case Expr::ObjCSubscriptRefExprClass:
124  case Expr::ObjCPropertyRefExprClass:
125  // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...
126  case Expr::CXXTypeidExprClass:
127  // Unresolved lookups and uncorrected typos get classified as lvalues.
128  // FIXME: Is this wise? Should they get their own kind?
129  case Expr::UnresolvedLookupExprClass:
130  case Expr::UnresolvedMemberExprClass:
131  case Expr::TypoExprClass:
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::OMPArraySectionExprClass:
142  return Cl::CL_LValue;
143 
144  // C99 6.5.2.5p5 says that compound literals are lvalues.
145  // In C++, they're prvalue temporaries, except for file-scope arrays.
146  case Expr::CompoundLiteralExprClass:
147  return !E->isLValue() ? ClassifyTemporary(E->getType()) : Cl::CL_LValue;
148 
149  // Expressions that are prvalues.
150  case Expr::CXXBoolLiteralExprClass:
151  case Expr::CXXPseudoDestructorExprClass:
152  case Expr::UnaryExprOrTypeTraitExprClass:
153  case Expr::CXXNewExprClass:
154  case Expr::CXXThisExprClass:
155  case Expr::CXXNullPtrLiteralExprClass:
156  case Expr::ImaginaryLiteralClass:
157  case Expr::GNUNullExprClass:
158  case Expr::OffsetOfExprClass:
159  case Expr::CXXThrowExprClass:
160  case Expr::ShuffleVectorExprClass:
161  case Expr::ConvertVectorExprClass:
162  case Expr::IntegerLiteralClass:
163  case Expr::FixedPointLiteralClass:
164  case Expr::CharacterLiteralClass:
165  case Expr::AddrLabelExprClass:
166  case Expr::CXXDeleteExprClass:
167  case Expr::ImplicitValueInitExprClass:
168  case Expr::BlockExprClass:
169  case Expr::FloatingLiteralClass:
170  case Expr::CXXNoexceptExprClass:
171  case Expr::CXXScalarValueInitExprClass:
172  case Expr::TypeTraitExprClass:
173  case Expr::ArrayTypeTraitExprClass:
174  case Expr::ExpressionTraitExprClass:
175  case Expr::ObjCSelectorExprClass:
176  case Expr::ObjCProtocolExprClass:
177  case Expr::ObjCStringLiteralClass:
178  case Expr::ObjCBoxedExprClass:
179  case Expr::ObjCArrayLiteralClass:
180  case Expr::ObjCDictionaryLiteralClass:
181  case Expr::ObjCBoolLiteralExprClass:
182  case Expr::ObjCAvailabilityCheckExprClass:
183  case Expr::ParenListExprClass:
184  case Expr::SizeOfPackExprClass:
185  case Expr::SubstNonTypeTemplateParmPackExprClass:
186  case Expr::AsTypeExprClass:
187  case Expr::ObjCIndirectCopyRestoreExprClass:
188  case Expr::AtomicExprClass:
189  case Expr::CXXFoldExprClass:
190  case Expr::ArrayInitLoopExprClass:
191  case Expr::ArrayInitIndexExprClass:
192  case Expr::NoInitExprClass:
193  case Expr::DesignatedInitUpdateExprClass:
194  case Expr::SourceLocExprClass:
195  case Expr::ConceptSpecializationExprClass:
196  return Cl::CL_PRValue;
197 
198  case Expr::ConstantExprClass:
199  return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr());
200 
201  // Next come the complicated cases.
202  case Expr::SubstNonTypeTemplateParmExprClass:
203  return ClassifyInternal(Ctx,
204  cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
205 
206  // C, C++98 [expr.sub]p1: The result is an lvalue of type "T".
207  // C++11 (DR1213): in the case of an array operand, the result is an lvalue
208  // if that operand is an lvalue and an xvalue otherwise.
209  // Subscripting vector types is more like member access.
210  case Expr::ArraySubscriptExprClass:
211  if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
212  return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
213  if (Lang.CPlusPlus11) {
214  // Step over the array-to-pointer decay if present, but not over the
215  // temporary materialization.
216  auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts();
217  if (Base->getType()->isArrayType())
218  return ClassifyInternal(Ctx, Base);
219  }
220  return Cl::CL_LValue;
221 
222  // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
223  // function or variable and a prvalue otherwise.
224  case Expr::DeclRefExprClass:
225  if (E->getType() == Ctx.UnknownAnyTy)
226  return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
228  return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
229 
230  // Member access is complex.
231  case Expr::MemberExprClass:
232  return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
233 
234  case Expr::UnaryOperatorClass:
235  switch (cast<UnaryOperator>(E)->getOpcode()) {
236  // C++ [expr.unary.op]p1: The unary * operator performs indirection:
237  // [...] the result is an lvalue referring to the object or function
238  // to which the expression points.
239  case UO_Deref:
240  return Cl::CL_LValue;
241 
242  // GNU extensions, simply look through them.
243  case UO_Extension:
244  return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
245 
246  // Treat _Real and _Imag basically as if they were member
247  // expressions: l-value only if the operand is a true l-value.
248  case UO_Real:
249  case UO_Imag: {
250  const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
251  Cl::Kinds K = ClassifyInternal(Ctx, Op);
252  if (K != Cl::CL_LValue) return K;
253 
254  if (isa<ObjCPropertyRefExpr>(Op))
256  return Cl::CL_LValue;
257  }
258 
259  // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
260  // lvalue, [...]
261  // Not so in C.
262  case UO_PreInc:
263  case UO_PreDec:
264  return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
265 
266  default:
267  return Cl::CL_PRValue;
268  }
269 
270  case Expr::OpaqueValueExprClass:
271  return ClassifyExprValueKind(Lang, E, E->getValueKind());
272 
273  // Pseudo-object expressions can produce l-values with reference magic.
274  case Expr::PseudoObjectExprClass:
275  return ClassifyExprValueKind(Lang, E,
276  cast<PseudoObjectExpr>(E)->getValueKind());
277 
278  // Implicit casts are lvalues if they're lvalue casts. Other than that, we
279  // only specifically record class temporaries.
280  case Expr::ImplicitCastExprClass:
281  return ClassifyExprValueKind(Lang, E, E->getValueKind());
282 
283  // C++ [expr.prim.general]p4: The presence of parentheses does not affect
284  // whether the expression is an lvalue.
285  case Expr::ParenExprClass:
286  return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
287 
288  // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
289  // or a void expression if its result expression is, respectively, an
290  // lvalue, a function designator, or a void expression.
291  case Expr::GenericSelectionExprClass:
292  if (cast<GenericSelectionExpr>(E)->isResultDependent())
293  return Cl::CL_PRValue;
294  return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
295 
296  case Expr::BinaryOperatorClass:
297  case Expr::CompoundAssignOperatorClass:
298  // C doesn't have any binary expressions that are lvalues.
299  if (Lang.CPlusPlus)
300  return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
301  return Cl::CL_PRValue;
302 
303  case Expr::CallExprClass:
304  case Expr::CXXOperatorCallExprClass:
305  case Expr::CXXMemberCallExprClass:
306  case Expr::UserDefinedLiteralClass:
307  case Expr::CUDAKernelCallExprClass:
308  return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
309 
310  case Expr::CXXRewrittenBinaryOperatorClass:
311  return ClassifyInternal(
312  Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm());
313 
314  // __builtin_choose_expr is equivalent to the chosen expression.
315  case Expr::ChooseExprClass:
316  return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
317 
318  // Extended vector element access is an lvalue unless there are duplicates
319  // in the shuffle expression.
320  case Expr::ExtVectorElementExprClass:
321  if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
323  if (cast<ExtVectorElementExpr>(E)->isArrow())
324  return Cl::CL_LValue;
325  return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
326 
327  // Simply look at the actual default argument.
328  case Expr::CXXDefaultArgExprClass:
329  return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
330 
331  // Same idea for default initializers.
332  case Expr::CXXDefaultInitExprClass:
333  return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
334 
335  // Same idea for temporary binding.
336  case Expr::CXXBindTemporaryExprClass:
337  return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
338 
339  // And the cleanups guard.
340  case Expr::ExprWithCleanupsClass:
341  return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
342 
343  // Casts depend completely on the target type. All casts work the same.
344  case Expr::CStyleCastExprClass:
345  case Expr::CXXFunctionalCastExprClass:
346  case Expr::CXXStaticCastExprClass:
347  case Expr::CXXDynamicCastExprClass:
348  case Expr::CXXReinterpretCastExprClass:
349  case Expr::CXXConstCastExprClass:
350  case Expr::ObjCBridgedCastExprClass:
351  case Expr::BuiltinBitCastExprClass:
352  // Only in C++ can casts be interesting at all.
353  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
354  return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
355 
356  case Expr::CXXUnresolvedConstructExprClass:
357  return ClassifyUnnamed(Ctx,
358  cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
359 
360  case Expr::BinaryConditionalOperatorClass: {
361  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
362  const auto *co = cast<BinaryConditionalOperator>(E);
363  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
364  }
365 
366  case Expr::ConditionalOperatorClass: {
367  // Once again, only C++ is interesting.
368  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
369  const auto *co = cast<ConditionalOperator>(E);
370  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
371  }
372 
373  // ObjC message sends are effectively function calls, if the target function
374  // is known.
375  case Expr::ObjCMessageExprClass:
376  if (const ObjCMethodDecl *Method =
377  cast<ObjCMessageExpr>(E)->getMethodDecl()) {
378  Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());
379  return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
380  }
381  return Cl::CL_PRValue;
382 
383  // Some C++ expressions are always class temporaries.
384  case Expr::CXXConstructExprClass:
385  case Expr::CXXInheritedCtorInitExprClass:
386  case Expr::CXXTemporaryObjectExprClass:
387  case Expr::LambdaExprClass:
388  case Expr::CXXStdInitializerListExprClass:
389  return Cl::CL_ClassTemporary;
390 
391  case Expr::VAArgExprClass:
392  return ClassifyUnnamed(Ctx, E->getType());
393 
394  case Expr::DesignatedInitExprClass:
395  return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
396 
397  case Expr::StmtExprClass: {
398  const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
399  if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
400  return ClassifyUnnamed(Ctx, LastExpr->getType());
401  return Cl::CL_PRValue;
402  }
403 
404  case Expr::CXXUuidofExprClass:
405  return Cl::CL_LValue;
406 
407  case Expr::PackExpansionExprClass:
408  return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
409 
410  case Expr::MaterializeTemporaryExprClass:
411  return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
412  ? Cl::CL_LValue
413  : Cl::CL_XValue;
414 
415  case Expr::InitListExprClass:
416  // An init list can be an lvalue if it is bound to a reference and
417  // contains only one element. In that case, we look at that element
418  // for an exact classification. Init list creation takes care of the
419  // value kind for us, so we only need to fine-tune.
420  if (E->isRValue())
421  return ClassifyExprValueKind(Lang, E, E->getValueKind());
422  assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
423  "Only 1-element init lists can be glvalues.");
424  return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
425 
426  case Expr::CoawaitExprClass:
427  case Expr::CoyieldExprClass:
428  return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr());
429  }
430 
431  llvm_unreachable("unhandled expression kind in classification");
432 }
433 
434 /// ClassifyDecl - Return the classification of an expression referencing the
435 /// given declaration.
436 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
437  // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
438  // function, variable, or data member and a prvalue otherwise.
439  // In C, functions are not lvalues.
440  // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
441  // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
442  // special-case this.
443 
444  if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
445  return Cl::CL_MemberFunction;
446 
447  bool islvalue;
448  if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))
449  islvalue = NTTParm->getType()->isReferenceType();
450  else
451  islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
452  isa<IndirectFieldDecl>(D) ||
453  isa<BindingDecl>(D) ||
454  (Ctx.getLangOpts().CPlusPlus &&
455  (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
456  isa<FunctionTemplateDecl>(D)));
457 
458  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
459 }
460 
461 /// ClassifyUnnamed - Return the classification of an expression yielding an
462 /// unnamed value of the given type. This applies in particular to function
463 /// calls and casts.
465  // In C, function calls are always rvalues.
466  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
467 
468  // C++ [expr.call]p10: A function call is an lvalue if the result type is an
469  // lvalue reference type or an rvalue reference to function type, an xvalue
470  // if the result type is an rvalue reference to object type, and a prvalue
471  // otherwise.
472  if (T->isLValueReferenceType())
473  return Cl::CL_LValue;
474  const auto *RV = T->getAs<RValueReferenceType>();
475  if (!RV) // Could still be a class temporary, though.
476  return ClassifyTemporary(T);
477 
478  return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
479 }
480 
482  if (E->getType() == Ctx.UnknownAnyTy)
483  return (isa<FunctionDecl>(E->getMemberDecl())
485 
486  // Handle C first, it's easier.
487  if (!Ctx.getLangOpts().CPlusPlus) {
488  // C99 6.5.2.3p3
489  // For dot access, the expression is an lvalue if the first part is. For
490  // arrow access, it always is an lvalue.
491  if (E->isArrow())
492  return Cl::CL_LValue;
493  // ObjC property accesses are not lvalues, but get special treatment.
494  Expr *Base = E->getBase()->IgnoreParens();
495  if (isa<ObjCPropertyRefExpr>(Base))
497  return ClassifyInternal(Ctx, Base);
498  }
499 
500  NamedDecl *Member = E->getMemberDecl();
501  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
502  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
503  // E1.E2 is an lvalue.
504  if (const auto *Value = dyn_cast<ValueDecl>(Member))
505  if (Value->getType()->isReferenceType())
506  return Cl::CL_LValue;
507 
508  // Otherwise, one of the following rules applies.
509  // -- If E2 is a static member [...] then E1.E2 is an lvalue.
510  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
511  return Cl::CL_LValue;
512 
513  // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
514  // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
515  // otherwise, it is a prvalue.
516  if (isa<FieldDecl>(Member)) {
517  // *E1 is an lvalue
518  if (E->isArrow())
519  return Cl::CL_LValue;
521  if (isa<ObjCPropertyRefExpr>(Base))
523  return ClassifyInternal(Ctx, E->getBase());
524  }
525 
526  // -- If E2 is a [...] member function, [...]
527  // -- If it refers to a static member function [...], then E1.E2 is an
528  // lvalue; [...]
529  // -- Otherwise [...] E1.E2 is a prvalue.
530  if (const auto *Method = dyn_cast<CXXMethodDecl>(Member))
531  return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
532 
533  // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
534  // So is everything else we haven't handled yet.
535  return Cl::CL_PRValue;
536 }
537 
539  assert(Ctx.getLangOpts().CPlusPlus &&
540  "This is only relevant for C++.");
541  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
542  // Except we override this for writes to ObjC properties.
543  if (E->isAssignmentOp())
544  return (E->getLHS()->getObjectKind() == OK_ObjCProperty
546 
547  // C++ [expr.comma]p1: the result is of the same value category as its right
548  // operand, [...].
549  if (E->getOpcode() == BO_Comma)
550  return ClassifyInternal(Ctx, E->getRHS());
551 
552  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
553  // is a pointer to a data member is of the same value category as its first
554  // operand.
555  if (E->getOpcode() == BO_PtrMemD)
556  return (E->getType()->isFunctionType() ||
557  E->hasPlaceholderType(BuiltinType::BoundMember))
559  : ClassifyInternal(Ctx, E->getLHS());
560 
561  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
562  // second operand is a pointer to data member and a prvalue otherwise.
563  if (E->getOpcode() == BO_PtrMemI)
564  return (E->getType()->isFunctionType() ||
565  E->hasPlaceholderType(BuiltinType::BoundMember))
567  : Cl::CL_LValue;
568 
569  // All other binary operations are prvalues.
570  return Cl::CL_PRValue;
571 }
572 
573 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
574  const Expr *False) {
575  assert(Ctx.getLangOpts().CPlusPlus &&
576  "This is only relevant for C++.");
577 
578  // C++ [expr.cond]p2
579  // If either the second or the third operand has type (cv) void,
580  // one of the following shall hold:
581  if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
582  // The second or the third operand (but not both) is a (possibly
583  // parenthesized) throw-expression; the result is of the [...] value
584  // category of the other.
585  bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
586  bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
587  if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
588  : (FalseIsThrow ? True : nullptr))
589  return ClassifyInternal(Ctx, NonThrow);
590 
591  // [Otherwise] the result [...] is a prvalue.
592  return Cl::CL_PRValue;
593  }
594 
595  // Note that at this point, we have already performed all conversions
596  // according to [expr.cond]p3.
597  // C++ [expr.cond]p4: If the second and third operands are glvalues of the
598  // same value category [...], the result is of that [...] value category.
599  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
600  Cl::Kinds LCl = ClassifyInternal(Ctx, True),
601  RCl = ClassifyInternal(Ctx, False);
602  return LCl == RCl ? LCl : Cl::CL_PRValue;
603 }
604 
606  Cl::Kinds Kind, SourceLocation &Loc) {
607  // As a general rule, we only care about lvalues. But there are some rvalues
608  // for which we want to generate special results.
609  if (Kind == Cl::CL_PRValue) {
610  // For the sake of better diagnostics, we want to specifically recognize
611  // use of the GCC cast-as-lvalue extension.
612  if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
613  if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
614  Loc = CE->getExprLoc();
615  return Cl::CM_LValueCast;
616  }
617  }
618  }
619  if (Kind != Cl::CL_LValue)
620  return Cl::CM_RValue;
621 
622  // This is the lvalue case.
623  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
624  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
625  return Cl::CM_Function;
626 
627  // Assignment to a property in ObjC is an implicit setter access. But a
628  // setter might not exist.
629  if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
630  if (Expr->isImplicitProperty() &&
631  Expr->getImplicitPropertySetter() == nullptr)
633  }
634 
635  CanQualType CT = Ctx.getCanonicalType(E->getType());
636  // Const stuff is obviously not modifiable.
637  if (CT.isConstQualified())
638  return Cl::CM_ConstQualified;
639  if (Ctx.getLangOpts().OpenCL &&
641  return Cl::CM_ConstAddrSpace;
642 
643  // Arrays are not modifiable, only their elements are.
644  if (CT->isArrayType())
645  return Cl::CM_ArrayType;
646  // Incomplete types are not modifiable.
647  if (CT->isIncompleteType())
648  return Cl::CM_IncompleteType;
649 
650  // Records with any const fields (recursively) are not modifiable.
651  if (const RecordType *R = CT->getAs<RecordType>())
652  if (R->hasConstFields())
654 
655  return Cl::CM_Modifiable;
656 }
657 
659  Classification VC = Classify(Ctx);
660  switch (VC.getKind()) {
661  case Cl::CL_LValue: return LV_Valid;
662  case Cl::CL_XValue: return LV_InvalidExpression;
663  case Cl::CL_Function: return LV_NotObjectType;
664  case Cl::CL_Void: return LV_InvalidExpression;
673  }
674  llvm_unreachable("Unhandled kind");
675 }
676 
679  SourceLocation dummy;
680  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
681  switch (VC.getKind()) {
682  case Cl::CL_LValue: break;
684  case Cl::CL_Function: return MLV_NotObjectType;
685  case Cl::CL_Void: return MLV_InvalidExpression;
693  case Cl::CL_PRValue:
694  return VC.getModifiable() == Cl::CM_LValueCast ?
696  }
697  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
698  switch (VC.getModifiable()) {
699  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
700  case Cl::CM_Modifiable: return MLV_Valid;
701  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
702  case Cl::CM_Function: return MLV_NotObjectType;
703  case Cl::CM_LValueCast:
704  llvm_unreachable("CM_LValueCast and CL_LValue don't match");
709  case Cl::CM_ArrayType: return MLV_ArrayType;
711  }
712  llvm_unreachable("Unhandled modifiable type");
713 }
Defines the clang::ASTContext interface.
Stmt * body_back()
Definition: Stmt.h:1358
A (possibly-)qualified type.
Definition: Type.h:643
bool isArrayType() const
Definition: Type.h:6447
ValueDecl * getMemberDecl() const
Retrieve the member declaration to which this expression refers.
Definition: Expr.h:2894
bool isConstQualified() const
bool hasPlaceholderType() const
Returns whether this expression has a placeholder type.
Definition: Expr.h:481
bool isRecordType() const
Definition: Type.h:6471
Expr * getBase() const
Definition: Expr.h:2888
Decl - This represents one declaration (or definition), e.g.
Definition: DeclBase.h:88
Defines the C++ template declaration subclasses.
Opcode getOpcode() const
Definition: Expr.h:3444
Classification Classify(ASTContext &Ctx) const
Classify - Classify this expression according to the C++11 expression taxonomy.
Definition: Expr.h:386
isModifiableLvalueResult
Definition: Expr.h:278
static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang, const Expr *E, ExprValueKind Kind)
const T * getAs() const
Member-template getAs<specific type>&#39;.
Definition: Type.h:6858
ObjCMethodDecl - Represents an instance or class method declaration.
Definition: DeclObjC.h:138
static bool isAssignmentOp(Opcode Opc)
Definition: Expr.h:3535
Defines the clang::Expr interface and subclasses for C++ expressions.
Qualifiers getQualifiers() const
Retrieve all qualifiers.
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:160
LValueClassification ClassifyLValue(ASTContext &Ctx) const
Reasons why an expression might not be an l-value.
static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E, Cl::Kinds Kind, SourceLocation &Loc)
bool isReferenceType() const
Definition: Type.h:6403
Classification ClassifyModifiable(ASTContext &Ctx, SourceLocation &Loc) const
ClassifyModifiable - Classify this expression according to the C++11 expression taxonomy, and see if it is valid on the left side of an assignment.
Definition: Expr.h:398
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:49
An r-value expression (a pr-value in the C++11 taxonomy) produces a temporary value.
Definition: Specifiers.h:125
An rvalue reference type, per C++11 [dcl.ref].
Definition: Type.h:2786
An x-value expression is a reference to an object with independent storage but which can be "moved"...
Definition: Specifiers.h:134
ExprValueKind getValueKind() const
getValueKind - The value kind that this expression produces.
Definition: Expr.h:414
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:3409
LangAS getAddressSpace() const
Definition: Type.h:353
bool isArrow() const
Definition: Expr.h:2995
CompoundStmt - This represents a group of statements like { stmt stmt }.
Definition: Stmt.h:1320
The return type of classify().
Definition: Expr.h:311
bool hasQualifiers() const
Determine whether this type has any qualifiers.
Definition: Type.h:6223
Kinds
The various classification results. Most of these mean prvalue.
Definition: Expr.h:314
An Objective-C property is a logical field of an Objective-C object which is read and written via Obj...
Definition: Specifiers.h:151
This represents one expression.
Definition: Expr.h:108
ExprValueKind
The categorization of expression values, currently following the C++11 scheme.
Definition: Specifiers.h:122
DeclContext * getDeclContext()
Definition: DeclBase.h:438
QualType getType() const
Definition: Expr.h:137
ModifiableType
The results of modification testing.
Definition: Expr.h:329
ExprObjectKind getObjectKind() const
getObjectKind - The object kind that this expression produces.
Definition: Expr.h:421
static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T)
ClassifyUnnamed - Return the classification of an expression yielding an unnamed value of the given t...
static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E)
CanQualType OverloadTy
Definition: ASTContext.h:1044
Kind
Encodes a location in the source.
bool isLValue() const
isLValue - True if this expression is an "l-value" according to the rules of the current language...
Definition: Expr.h:258
isModifiableLvalueResult isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc=nullptr) const
isModifiableLvalue - C99 6.3.2.1: an lvalue that does not have array type, does not have an incomplet...
static Cl::Kinds ClassifyTemporary(QualType T)
Classify an expression which creates a temporary, based on its type.
CanProxy< U > getAs() const
Retrieve a canonical type pointer with a different static type, upcasting or downcasting as needed...
Expr * getLHS() const
Definition: Expr.h:3449
static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E)
Dataflow Directional Tag Classes.
ModifiableType getModifiable() const
Definition: Expr.h:357
bool isRecord() const
Definition: DeclBase.h:1858
static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D)
ClassifyDecl - Return the classification of an expression referencing the given declaration.
StmtClass getStmtClass() const
Definition: Stmt.h:1097
Kinds getKind() const
Definition: Expr.h:356
static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *trueExpr, const Expr *falseExpr)
Expr * IgnoreParenImpCasts() LLVM_READONLY
Skip past any parentheses and implicit casts which might surround this expression until reaching a fi...
Definition: Expr.cpp:2966
A helper class that allows the use of isa/cast/dyncast to detect TagType objects of structs/unions/cl...
Definition: Type.h:4444
CanQualType UnknownAnyTy
Definition: ASTContext.h:1044
bool isFunctionType() const
Definition: Type.h:6387
LValueClassification
Definition: Expr.h:263
CanQualType getCanonicalType(QualType T) const
Return the canonical (structural) type corresponding to the specified potentially non-canonical type ...
Definition: ASTContext.h:2289
bool isLValueReferenceType() const
Definition: Type.h:6407
Defines the C++ Decl subclasses, other than those for templates (found in DeclTemplate.h) and friends (in DeclFriend.h).
MemberExpr - [C99 6.5.2.3] Structure and Union Members.
Definition: Expr.h:2811
bool isVoidType() const
Definition: Type.h:6650
bool isRValue() const
Definition: Expr.h:259
unsigned kind
All of the diagnostics that can be emitted by the frontend.
Definition: DiagnosticIDs.h:60
static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E)
Expr * getRHS() const
Definition: Expr.h:3451
An l-value expression is a reference to an object with independent storage.
Definition: Specifiers.h:129
This represents a decl that may have a name.
Definition: Decl.h:248
const LangOptions & getLangOpts() const
Definition: ASTContext.h:723
Expr * IgnoreParens() LLVM_READONLY
Skip past any parentheses which might surround this expression until reaching a fixed point...
Definition: Expr.cpp:2962