clang  3.7.0
ExprClassification.cpp
Go to the documentation of this file.
1 //===--- ExprClassification.cpp - Expression AST Node Implementation ------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements Expr::classify.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "clang/AST/Expr.h"
15 #include "clang/AST/ASTContext.h"
16 #include "clang/AST/DeclCXX.h"
17 #include "clang/AST/DeclObjC.h"
18 #include "clang/AST/DeclTemplate.h"
19 #include "clang/AST/ExprCXX.h"
20 #include "clang/AST/ExprObjC.h"
21 #include "llvm/Support/ErrorHandling.h"
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::CXXDependentScopeMemberExprClass:
133  case Expr::DependentScopeDeclRefExprClass:
134  // ObjC instance variables are lvalues
135  // FIXME: ObjC++0x might have different rules
136  case Expr::ObjCIvarRefExprClass:
137  case Expr::FunctionParmPackExprClass:
138  case Expr::MSPropertyRefExprClass:
139  return Cl::CL_LValue;
140 
141  // C99 6.5.2.5p5 says that compound literals are lvalues.
142  // In C++, they're prvalue temporaries.
143  case Expr::CompoundLiteralExprClass:
144  return Ctx.getLangOpts().CPlusPlus ? ClassifyTemporary(E->getType())
145  : Cl::CL_LValue;
146 
147  // Expressions that are prvalues.
148  case Expr::CXXBoolLiteralExprClass:
149  case Expr::CXXPseudoDestructorExprClass:
150  case Expr::UnaryExprOrTypeTraitExprClass:
151  case Expr::CXXNewExprClass:
152  case Expr::CXXThisExprClass:
153  case Expr::CXXNullPtrLiteralExprClass:
154  case Expr::ImaginaryLiteralClass:
155  case Expr::GNUNullExprClass:
156  case Expr::OffsetOfExprClass:
157  case Expr::CXXThrowExprClass:
158  case Expr::ShuffleVectorExprClass:
159  case Expr::ConvertVectorExprClass:
160  case Expr::IntegerLiteralClass:
161  case Expr::CharacterLiteralClass:
162  case Expr::AddrLabelExprClass:
163  case Expr::CXXDeleteExprClass:
164  case Expr::ImplicitValueInitExprClass:
165  case Expr::BlockExprClass:
166  case Expr::FloatingLiteralClass:
167  case Expr::CXXNoexceptExprClass:
168  case Expr::CXXScalarValueInitExprClass:
169  case Expr::TypeTraitExprClass:
170  case Expr::ArrayTypeTraitExprClass:
171  case Expr::ExpressionTraitExprClass:
172  case Expr::ObjCSelectorExprClass:
173  case Expr::ObjCProtocolExprClass:
174  case Expr::ObjCStringLiteralClass:
175  case Expr::ObjCBoxedExprClass:
176  case Expr::ObjCArrayLiteralClass:
177  case Expr::ObjCDictionaryLiteralClass:
178  case Expr::ObjCBoolLiteralExprClass:
179  case Expr::ParenListExprClass:
180  case Expr::SizeOfPackExprClass:
181  case Expr::SubstNonTypeTemplateParmPackExprClass:
182  case Expr::AsTypeExprClass:
183  case Expr::ObjCIndirectCopyRestoreExprClass:
184  case Expr::AtomicExprClass:
185  case Expr::CXXFoldExprClass:
186  case Expr::NoInitExprClass:
187  case Expr::DesignatedInitUpdateExprClass:
188  return Cl::CL_PRValue;
189 
190  // Next come the complicated cases.
191  case Expr::SubstNonTypeTemplateParmExprClass:
192  return ClassifyInternal(Ctx,
193  cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
194 
195  // C++ [expr.sub]p1: The result is an lvalue of type "T".
196  // However, subscripting vector types is more like member access.
197  case Expr::ArraySubscriptExprClass:
198  if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
199  return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
200  return Cl::CL_LValue;
201 
202  // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
203  // function or variable and a prvalue otherwise.
204  case Expr::DeclRefExprClass:
205  if (E->getType() == Ctx.UnknownAnyTy)
206  return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
208  return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
209 
210  // Member access is complex.
211  case Expr::MemberExprClass:
212  return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
213 
214  case Expr::UnaryOperatorClass:
215  switch (cast<UnaryOperator>(E)->getOpcode()) {
216  // C++ [expr.unary.op]p1: The unary * operator performs indirection:
217  // [...] the result is an lvalue referring to the object or function
218  // to which the expression points.
219  case UO_Deref:
220  return Cl::CL_LValue;
221 
222  // GNU extensions, simply look through them.
223  case UO_Extension:
224  return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
225 
226  // Treat _Real and _Imag basically as if they were member
227  // expressions: l-value only if the operand is a true l-value.
228  case UO_Real:
229  case UO_Imag: {
230  const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
231  Cl::Kinds K = ClassifyInternal(Ctx, Op);
232  if (K != Cl::CL_LValue) return K;
233 
234  if (isa<ObjCPropertyRefExpr>(Op))
236  return Cl::CL_LValue;
237  }
238 
239  // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
240  // lvalue, [...]
241  // Not so in C.
242  case UO_PreInc:
243  case UO_PreDec:
244  return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
245 
246  default:
247  return Cl::CL_PRValue;
248  }
249 
250  case Expr::OpaqueValueExprClass:
251  return ClassifyExprValueKind(Lang, E, E->getValueKind());
252 
253  // Pseudo-object expressions can produce l-values with reference magic.
254  case Expr::PseudoObjectExprClass:
255  return ClassifyExprValueKind(Lang, E,
256  cast<PseudoObjectExpr>(E)->getValueKind());
257 
258  // Implicit casts are lvalues if they're lvalue casts. Other than that, we
259  // only specifically record class temporaries.
260  case Expr::ImplicitCastExprClass:
261  return ClassifyExprValueKind(Lang, E, E->getValueKind());
262 
263  // C++ [expr.prim.general]p4: The presence of parentheses does not affect
264  // whether the expression is an lvalue.
265  case Expr::ParenExprClass:
266  return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
267 
268  // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
269  // or a void expression if its result expression is, respectively, an
270  // lvalue, a function designator, or a void expression.
271  case Expr::GenericSelectionExprClass:
272  if (cast<GenericSelectionExpr>(E)->isResultDependent())
273  return Cl::CL_PRValue;
274  return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
275 
276  case Expr::BinaryOperatorClass:
277  case Expr::CompoundAssignOperatorClass:
278  // C doesn't have any binary expressions that are lvalues.
279  if (Lang.CPlusPlus)
280  return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
281  return Cl::CL_PRValue;
282 
283  case Expr::CallExprClass:
284  case Expr::CXXOperatorCallExprClass:
285  case Expr::CXXMemberCallExprClass:
286  case Expr::UserDefinedLiteralClass:
287  case Expr::CUDAKernelCallExprClass:
288  return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
289 
290  // __builtin_choose_expr is equivalent to the chosen expression.
291  case Expr::ChooseExprClass:
292  return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
293 
294  // Extended vector element access is an lvalue unless there are duplicates
295  // in the shuffle expression.
296  case Expr::ExtVectorElementExprClass:
297  if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
299  if (cast<ExtVectorElementExpr>(E)->isArrow())
300  return Cl::CL_LValue;
301  return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
302 
303  // Simply look at the actual default argument.
304  case Expr::CXXDefaultArgExprClass:
305  return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
306 
307  // Same idea for default initializers.
308  case Expr::CXXDefaultInitExprClass:
309  return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
310 
311  // Same idea for temporary binding.
312  case Expr::CXXBindTemporaryExprClass:
313  return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
314 
315  // And the cleanups guard.
316  case Expr::ExprWithCleanupsClass:
317  return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
318 
319  // Casts depend completely on the target type. All casts work the same.
320  case Expr::CStyleCastExprClass:
321  case Expr::CXXFunctionalCastExprClass:
322  case Expr::CXXStaticCastExprClass:
323  case Expr::CXXDynamicCastExprClass:
324  case Expr::CXXReinterpretCastExprClass:
325  case Expr::CXXConstCastExprClass:
326  case Expr::ObjCBridgedCastExprClass:
327  // Only in C++ can casts be interesting at all.
328  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
329  return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
330 
331  case Expr::CXXUnresolvedConstructExprClass:
332  return ClassifyUnnamed(Ctx,
333  cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
334 
335  case Expr::BinaryConditionalOperatorClass: {
336  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
337  const BinaryConditionalOperator *co = cast<BinaryConditionalOperator>(E);
338  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
339  }
340 
341  case Expr::ConditionalOperatorClass: {
342  // Once again, only C++ is interesting.
343  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
344  const ConditionalOperator *co = cast<ConditionalOperator>(E);
345  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
346  }
347 
348  // ObjC message sends are effectively function calls, if the target function
349  // is known.
350  case Expr::ObjCMessageExprClass:
351  if (const ObjCMethodDecl *Method =
352  cast<ObjCMessageExpr>(E)->getMethodDecl()) {
353  Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());
354  return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
355  }
356  return Cl::CL_PRValue;
357 
358  // Some C++ expressions are always class temporaries.
359  case Expr::CXXConstructExprClass:
360  case Expr::CXXTemporaryObjectExprClass:
361  case Expr::LambdaExprClass:
362  case Expr::CXXStdInitializerListExprClass:
363  return Cl::CL_ClassTemporary;
364 
365  case Expr::VAArgExprClass:
366  return ClassifyUnnamed(Ctx, E->getType());
367 
368  case Expr::DesignatedInitExprClass:
369  return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
370 
371  case Expr::StmtExprClass: {
372  const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
373  if (const Expr *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
374  return ClassifyUnnamed(Ctx, LastExpr->getType());
375  return Cl::CL_PRValue;
376  }
377 
378  case Expr::CXXUuidofExprClass:
379  return Cl::CL_LValue;
380 
381  case Expr::PackExpansionExprClass:
382  return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
383 
384  case Expr::MaterializeTemporaryExprClass:
385  return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
386  ? Cl::CL_LValue
387  : Cl::CL_XValue;
388 
389  case Expr::InitListExprClass:
390  // An init list can be an lvalue if it is bound to a reference and
391  // contains only one element. In that case, we look at that element
392  // for an exact classification. Init list creation takes care of the
393  // value kind for us, so we only need to fine-tune.
394  if (E->isRValue())
395  return ClassifyExprValueKind(Lang, E, E->getValueKind());
396  assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
397  "Only 1-element init lists can be glvalues.");
398  return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
399  }
400 
401  llvm_unreachable("unhandled expression kind in classification");
402 }
403 
404 /// ClassifyDecl - Return the classification of an expression referencing the
405 /// given declaration.
406 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
407  // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
408  // function, variable, or data member and a prvalue otherwise.
409  // In C, functions are not lvalues.
410  // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
411  // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
412  // special-case this.
413 
414  if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
415  return Cl::CL_MemberFunction;
416 
417  bool islvalue;
418  if (const NonTypeTemplateParmDecl *NTTParm =
419  dyn_cast<NonTypeTemplateParmDecl>(D))
420  islvalue = NTTParm->getType()->isReferenceType();
421  else
422  islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
423  isa<IndirectFieldDecl>(D) ||
424  (Ctx.getLangOpts().CPlusPlus &&
425  (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
426  isa<FunctionTemplateDecl>(D)));
427 
428  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
429 }
430 
431 /// ClassifyUnnamed - Return the classification of an expression yielding an
432 /// unnamed value of the given type. This applies in particular to function
433 /// calls and casts.
435  // In C, function calls are always rvalues.
436  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
437 
438  // C++ [expr.call]p10: A function call is an lvalue if the result type is an
439  // lvalue reference type or an rvalue reference to function type, an xvalue
440  // if the result type is an rvalue reference to object type, and a prvalue
441  // otherwise.
442  if (T->isLValueReferenceType())
443  return Cl::CL_LValue;
445  if (!RV) // Could still be a class temporary, though.
446  return ClassifyTemporary(T);
447 
449 }
450 
452  if (E->getType() == Ctx.UnknownAnyTy)
453  return (isa<FunctionDecl>(E->getMemberDecl())
455 
456  // Handle C first, it's easier.
457  if (!Ctx.getLangOpts().CPlusPlus) {
458  // C99 6.5.2.3p3
459  // For dot access, the expression is an lvalue if the first part is. For
460  // arrow access, it always is an lvalue.
461  if (E->isArrow())
462  return Cl::CL_LValue;
463  // ObjC property accesses are not lvalues, but get special treatment.
464  Expr *Base = E->getBase()->IgnoreParens();
465  if (isa<ObjCPropertyRefExpr>(Base))
467  return ClassifyInternal(Ctx, Base);
468  }
469 
470  NamedDecl *Member = E->getMemberDecl();
471  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
472  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
473  // E1.E2 is an lvalue.
474  if (ValueDecl *Value = dyn_cast<ValueDecl>(Member))
475  if (Value->getType()->isReferenceType())
476  return Cl::CL_LValue;
477 
478  // Otherwise, one of the following rules applies.
479  // -- If E2 is a static member [...] then E1.E2 is an lvalue.
480  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
481  return Cl::CL_LValue;
482 
483  // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
484  // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
485  // otherwise, it is a prvalue.
486  if (isa<FieldDecl>(Member)) {
487  // *E1 is an lvalue
488  if (E->isArrow())
489  return Cl::CL_LValue;
491  if (isa<ObjCPropertyRefExpr>(Base))
493  return ClassifyInternal(Ctx, E->getBase());
494  }
495 
496  // -- If E2 is a [...] member function, [...]
497  // -- If it refers to a static member function [...], then E1.E2 is an
498  // lvalue; [...]
499  // -- Otherwise [...] E1.E2 is a prvalue.
500  if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member))
501  return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
502 
503  // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
504  // So is everything else we haven't handled yet.
505  return Cl::CL_PRValue;
506 }
507 
509  assert(Ctx.getLangOpts().CPlusPlus &&
510  "This is only relevant for C++.");
511  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
512  // Except we override this for writes to ObjC properties.
513  if (E->isAssignmentOp())
514  return (E->getLHS()->getObjectKind() == OK_ObjCProperty
516 
517  // C++ [expr.comma]p1: the result is of the same value category as its right
518  // operand, [...].
519  if (E->getOpcode() == BO_Comma)
520  return ClassifyInternal(Ctx, E->getRHS());
521 
522  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
523  // is a pointer to a data member is of the same value category as its first
524  // operand.
525  if (E->getOpcode() == BO_PtrMemD)
526  return (E->getType()->isFunctionType() ||
527  E->hasPlaceholderType(BuiltinType::BoundMember))
529  : ClassifyInternal(Ctx, E->getLHS());
530 
531  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
532  // second operand is a pointer to data member and a prvalue otherwise.
533  if (E->getOpcode() == BO_PtrMemI)
534  return (E->getType()->isFunctionType() ||
535  E->hasPlaceholderType(BuiltinType::BoundMember))
537  : Cl::CL_LValue;
538 
539  // All other binary operations are prvalues.
540  return Cl::CL_PRValue;
541 }
542 
543 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
544  const Expr *False) {
545  assert(Ctx.getLangOpts().CPlusPlus &&
546  "This is only relevant for C++.");
547 
548  // C++ [expr.cond]p2
549  // If either the second or the third operand has type (cv) void,
550  // one of the following shall hold:
551  if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
552  // The second or the third operand (but not both) is a (possibly
553  // parenthesized) throw-expression; the result is of the [...] value
554  // category of the other.
555  bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
556  bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
557  if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
558  : (FalseIsThrow ? True : nullptr))
559  return ClassifyInternal(Ctx, NonThrow);
560 
561  // [Otherwise] the result [...] is a prvalue.
562  return Cl::CL_PRValue;
563  }
564 
565  // Note that at this point, we have already performed all conversions
566  // according to [expr.cond]p3.
567  // C++ [expr.cond]p4: If the second and third operands are glvalues of the
568  // same value category [...], the result is of that [...] value category.
569  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
570  Cl::Kinds LCl = ClassifyInternal(Ctx, True),
571  RCl = ClassifyInternal(Ctx, False);
572  return LCl == RCl ? LCl : Cl::CL_PRValue;
573 }
574 
576  Cl::Kinds Kind, SourceLocation &Loc) {
577  // As a general rule, we only care about lvalues. But there are some rvalues
578  // for which we want to generate special results.
579  if (Kind == Cl::CL_PRValue) {
580  // For the sake of better diagnostics, we want to specifically recognize
581  // use of the GCC cast-as-lvalue extension.
582  if (const ExplicitCastExpr *CE =
583  dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
584  if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
585  Loc = CE->getExprLoc();
586  return Cl::CM_LValueCast;
587  }
588  }
589  }
590  if (Kind != Cl::CL_LValue)
591  return Cl::CM_RValue;
592 
593  // This is the lvalue case.
594  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
595  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
596  return Cl::CM_Function;
597 
598  // Assignment to a property in ObjC is an implicit setter access. But a
599  // setter might not exist.
600  if (const ObjCPropertyRefExpr *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
601  if (Expr->isImplicitProperty() &&
602  Expr->getImplicitPropertySetter() == nullptr)
604  }
605 
606  CanQualType CT = Ctx.getCanonicalType(E->getType());
607  // Const stuff is obviously not modifiable.
608  if (CT.isConstQualified())
609  return Cl::CM_ConstQualified;
611  return Cl::CM_ConstAddrSpace;
612 
613  // Arrays are not modifiable, only their elements are.
614  if (CT->isArrayType())
615  return Cl::CM_ArrayType;
616  // Incomplete types are not modifiable.
617  if (CT->isIncompleteType())
618  return Cl::CM_IncompleteType;
619 
620  // Records with any const fields (recursively) are not modifiable.
621  if (const RecordType *R = CT->getAs<RecordType>())
622  if (R->hasConstFields())
623  return Cl::CM_ConstQualified;
624 
625  return Cl::CM_Modifiable;
626 }
627 
629  Classification VC = Classify(Ctx);
630  switch (VC.getKind()) {
631  case Cl::CL_LValue: return LV_Valid;
632  case Cl::CL_XValue: return LV_InvalidExpression;
633  case Cl::CL_Function: return LV_NotObjectType;
634  case Cl::CL_Void: return LV_InvalidExpression;
643  }
644  llvm_unreachable("Unhandled kind");
645 }
646 
649  SourceLocation dummy;
650  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
651  switch (VC.getKind()) {
652  case Cl::CL_LValue: break;
654  case Cl::CL_Function: return MLV_NotObjectType;
655  case Cl::CL_Void: return MLV_InvalidExpression;
663  case Cl::CL_PRValue:
664  return VC.getModifiable() == Cl::CM_LValueCast ?
666  }
667  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
668  switch (VC.getModifiable()) {
669  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
670  case Cl::CM_Modifiable: return MLV_Valid;
671  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
672  case Cl::CM_Function: return MLV_NotObjectType;
673  case Cl::CM_LValueCast:
674  llvm_unreachable("CM_LValueCast and CL_LValue don't match");
678  case Cl::CM_ArrayType: return MLV_ArrayType;
680  }
681  llvm_unreachable("Unhandled modifiable type");
682 }
LValueClassification ClassifyLValue(ASTContext &Ctx) const
Reasons why an expression might not be an l-value.
ValueDecl * getMemberDecl() const
Retrieve the member declaration to which this expression refers.
Definition: Expr.h:2411
Defines the clang::ASTContext interface.
ExprObjectKind getObjectKind() const
Definition: Expr.h:411
Stmt * body_back()
Definition: Stmt.h:589
bool hasPlaceholderType() const
Returns whether this expression has a placeholder type.
Definition: Expr.h:462
bool isRecordType() const
Definition: Type.h:5289
Defines the C++ template declaration subclasses.
bool isConstQualified() const
isModifiableLvalueResult
Definition: Expr.h:270
static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang, const Expr *E, ExprValueKind Kind)
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:388
static bool isAssignmentOp(Opcode Opc)
Definition: Expr.h:3040
Defines the clang::Expr interface and subclasses for C++ expressions.
bool isVoidType() const
Definition: Type.h:5426
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:89
bool isReferenceType() const
Definition: Type.h:5241
static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E, Cl::Kinds Kind, SourceLocation &Loc)
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:48
Expr::Classification Cl
An r-value expression (a pr-value in the C++11 taxonomy) produces a temporary value.
Definition: Specifiers.h:95
Expr * getLHS() const
Definition: Expr.h:2964
const LangOptions & getLangOpts() const
Definition: ASTContext.h:533
CanProxy< U > getAs() const
Retrieve a canonical type pointer with a different static type, upcasting or downcasting as needed...
An x-value expression is a reference to an object with independent storage but which can be "moved"...
Definition: Specifiers.h:104
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:2918
Expr * getFalseExpr() const
Definition: Expr.h:3231
The return type of classify(). Represents the C++11 expression taxonomy.
Definition: Expr.h:302
Kinds
The various classification results. Most of these mean prvalue.
Definition: Expr.h:305
ExprValueKind
The categorization of expression values, currently following the C++11 scheme.
Definition: Specifiers.h:92
Qualifiers getQualifiers() const
Retrieve all qualifiers.
Kinds getKind() const
Definition: Expr.h:346
DeclContext * getDeclContext()
Definition: DeclBase.h:381
Classification Classify(ASTContext &Ctx) const
Classify - Classify this expression according to the C++11 expression taxonomy.
Definition: Expr.h:376
isModifiableLvalueResult isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc=nullptr) const
ModifiableType
The results of modification testing.
Definition: Expr.h:320
Expr * getTrueExpr() const
Definition: Expr.h:3226
static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T)
static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E)
CanQualType OverloadTy
Definition: ASTContext.h:832
Kind
Encodes a location in the source. The SourceManager can decode this to get at the full include stack...
Represents a static or instance method of a struct/union/class.
Definition: DeclCXX.h:1717
bool isRValue() const
Definition: Expr.h:251
static Cl::Kinds ClassifyTemporary(QualType T)
Classify an expression which creates a temporary, based on its type.
static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E)
bool isArrow() const
Definition: Expr.h:2548
QualType getType() const
Definition: Expr.h:125
static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D)
ModifiableType getModifiable() const
Definition: Expr.h:347
CanQualType getCanonicalType(QualType T) const
Return the canonical (structural) type corresponding to the specified potentially non-canonical type ...
Definition: ASTContext.h:1855
bool isLValueReferenceType() const
Definition: Type.h:5244
static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *trueExpr, const Expr *falseExpr)
Expr * IgnoreParenImpCasts() LLVM_READONLY
Definition: Expr.cpp:2526
CanQualType UnknownAnyTy
Definition: ASTContext.h:832
const T * getAs() const
Definition: Type.h:5555
bool isFunctionType() const
Definition: Type.h:5229
LValueClassification
Definition: Expr.h:255
unsigned getAddressSpace() const
Definition: Type.h:313
QualType getPointeeType() const
Definition: Type.h:2286
Expr * getFalseExpr() const
getFalseExpr - Return the subexpression which will be evaluated if the condnition evaluates to false;...
Definition: Expr.h:3317
Expr * getBase() const
Definition: Expr.h:2405
Defines the C++ Decl subclasses, other than those for templates (found in DeclTemplate.h) and friends (in DeclFriend.h).
Opcode getOpcode() const
Definition: Expr.h:2961
unsigned kind
All of the diagnostics that can be emitted by the frontend.
Definition: DiagnosticIDs.h:43
bool isArrayType() const
Definition: Type.h:5271
Expr * getRHS() const
Definition: Expr.h:2966
bool isRecord() const
Definition: DeclBase.h:1247
static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E)
ExprValueKind getValueKind() const
getValueKind - The value kind that this expression produces.
Definition: Expr.h:404
bool hasQualifiers() const
Determine whether this type has any qualifiers.
Definition: Type.h:5091
Expr * getTrueExpr() const
getTrueExpr - Return the subexpression which will be evaluated if the condition evaluates to true; th...
Definition: Expr.h:3310
An l-value expression is a reference to an object with independent storage.
Definition: Specifiers.h:99
Expr * IgnoreParens() LLVM_READONLY
Definition: Expr.cpp:2408