clang  8.0.0svn
ExprClassification.cpp
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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 
23 using namespace clang;
24 
26 
27 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E);
28 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D);
30 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E);
33  const Expr *trueExpr,
34  const Expr *falseExpr);
35 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
37 
38 Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {
39  assert(!TR->isReferenceType() && "Expressions can't have reference type.");
40 
41  Cl::Kinds kind = ClassifyInternal(Ctx, this);
42  // C99 6.3.2.1: An lvalue is an expression with an object type or an
43  // incomplete type other than void.
44  if (!Ctx.getLangOpts().CPlusPlus) {
45  // Thus, no functions.
46  if (TR->isFunctionType() || TR == Ctx.OverloadTy)
47  kind = Cl::CL_Function;
48  // No void either, but qualified void is OK because it is "other than void".
49  // Void "lvalues" are classified as addressable void values, which are void
50  // expressions whose address can be taken.
51  else if (TR->isVoidType() && !TR.hasQualifiers())
53  }
54 
55  // Enable this assertion for testing.
56  switch (kind) {
57  case Cl::CL_LValue: assert(getValueKind() == VK_LValue); break;
58  case Cl::CL_XValue: assert(getValueKind() == VK_XValue); break;
59  case Cl::CL_Function:
60  case Cl::CL_Void:
68  case Cl::CL_PRValue: assert(getValueKind() == VK_RValue); break;
69  }
70 
72  if (Loc)
73  modifiable = IsModifiable(Ctx, this, kind, *Loc);
74  return Classification(kind, modifiable);
75 }
76 
77 /// Classify an expression which creates a temporary, based on its type.
79  if (T->isRecordType())
80  return Cl::CL_ClassTemporary;
81  if (T->isArrayType())
82  return Cl::CL_ArrayTemporary;
83 
84  // No special classification: these don't behave differently from normal
85  // prvalues.
86  return Cl::CL_PRValue;
87 }
88 
90  const Expr *E,
92  switch (Kind) {
93  case VK_RValue:
94  return Lang.CPlusPlus ? ClassifyTemporary(E->getType()) : Cl::CL_PRValue;
95  case VK_LValue:
96  return Cl::CL_LValue;
97  case VK_XValue:
98  return Cl::CL_XValue;
99  }
100  llvm_unreachable("Invalid value category of implicit cast.");
101 }
102 
103 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
104  // This function takes the first stab at classifying expressions.
105  const LangOptions &Lang = Ctx.getLangOpts();
106 
107  switch (E->getStmtClass()) {
108  case Stmt::NoStmtClass:
109 #define ABSTRACT_STMT(Kind)
110 #define STMT(Kind, Base) case Expr::Kind##Class:
111 #define EXPR(Kind, Base)
112 #include "clang/AST/StmtNodes.inc"
113  llvm_unreachable("cannot classify a statement");
114 
115  // First come the expressions that are always lvalues, unconditionally.
116  case Expr::ObjCIsaExprClass:
117  // C++ [expr.prim.general]p1: A string literal is an lvalue.
118  case Expr::StringLiteralClass:
119  // @encode is equivalent to its string
120  case Expr::ObjCEncodeExprClass:
121  // __func__ and friends are too.
122  case Expr::PredefinedExprClass:
123  // Property references are lvalues
124  case Expr::ObjCSubscriptRefExprClass:
125  case Expr::ObjCPropertyRefExprClass:
126  // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...
127  case Expr::CXXTypeidExprClass:
128  // Unresolved lookups and uncorrected typos get classified as lvalues.
129  // FIXME: Is this wise? Should they get their own kind?
130  case Expr::UnresolvedLookupExprClass:
131  case Expr::UnresolvedMemberExprClass:
132  case Expr::TypoExprClass:
133  case Expr::DependentCoawaitExprClass:
134  case Expr::CXXDependentScopeMemberExprClass:
135  case Expr::DependentScopeDeclRefExprClass:
136  // ObjC instance variables are lvalues
137  // FIXME: ObjC++0x might have different rules
138  case Expr::ObjCIvarRefExprClass:
139  case Expr::FunctionParmPackExprClass:
140  case Expr::MSPropertyRefExprClass:
141  case Expr::MSPropertySubscriptExprClass:
142  case Expr::OMPArraySectionExprClass:
143  return Cl::CL_LValue;
144 
145  // C99 6.5.2.5p5 says that compound literals are lvalues.
146  // In C++, they're prvalue temporaries, except for file-scope arrays.
147  case Expr::CompoundLiteralExprClass:
148  return !E->isLValue() ? ClassifyTemporary(E->getType()) : Cl::CL_LValue;
149 
150  // Expressions that are prvalues.
151  case Expr::CXXBoolLiteralExprClass:
152  case Expr::CXXPseudoDestructorExprClass:
153  case Expr::UnaryExprOrTypeTraitExprClass:
154  case Expr::CXXNewExprClass:
155  case Expr::CXXThisExprClass:
156  case Expr::CXXNullPtrLiteralExprClass:
157  case Expr::ImaginaryLiteralClass:
158  case Expr::GNUNullExprClass:
159  case Expr::OffsetOfExprClass:
160  case Expr::CXXThrowExprClass:
161  case Expr::ShuffleVectorExprClass:
162  case Expr::ConvertVectorExprClass:
163  case Expr::IntegerLiteralClass:
164  case Expr::FixedPointLiteralClass:
165  case Expr::CharacterLiteralClass:
166  case Expr::AddrLabelExprClass:
167  case Expr::CXXDeleteExprClass:
168  case Expr::ImplicitValueInitExprClass:
169  case Expr::BlockExprClass:
170  case Expr::FloatingLiteralClass:
171  case Expr::CXXNoexceptExprClass:
172  case Expr::CXXScalarValueInitExprClass:
173  case Expr::TypeTraitExprClass:
174  case Expr::ArrayTypeTraitExprClass:
175  case Expr::ExpressionTraitExprClass:
176  case Expr::ObjCSelectorExprClass:
177  case Expr::ObjCProtocolExprClass:
178  case Expr::ObjCStringLiteralClass:
179  case Expr::ObjCBoxedExprClass:
180  case Expr::ObjCArrayLiteralClass:
181  case Expr::ObjCDictionaryLiteralClass:
182  case Expr::ObjCBoolLiteralExprClass:
183  case Expr::ObjCAvailabilityCheckExprClass:
184  case Expr::ParenListExprClass:
185  case Expr::SizeOfPackExprClass:
186  case Expr::SubstNonTypeTemplateParmPackExprClass:
187  case Expr::AsTypeExprClass:
188  case Expr::ObjCIndirectCopyRestoreExprClass:
189  case Expr::AtomicExprClass:
190  case Expr::CXXFoldExprClass:
191  case Expr::ArrayInitLoopExprClass:
192  case Expr::ArrayInitIndexExprClass:
193  case Expr::NoInitExprClass:
194  case Expr::DesignatedInitUpdateExprClass:
195  return Cl::CL_PRValue;
196 
197  // Next come the complicated cases.
198  case Expr::SubstNonTypeTemplateParmExprClass:
199  return ClassifyInternal(Ctx,
200  cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
201 
202  // C, C++98 [expr.sub]p1: The result is an lvalue of type "T".
203  // C++11 (DR1213): in the case of an array operand, the result is an lvalue
204  // if that operand is an lvalue and an xvalue otherwise.
205  // Subscripting vector types is more like member access.
206  case Expr::ArraySubscriptExprClass:
207  if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
208  return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
209  if (Lang.CPlusPlus11) {
210  // Step over the array-to-pointer decay if present, but not over the
211  // temporary materialization.
212  auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts();
213  if (Base->getType()->isArrayType())
214  return ClassifyInternal(Ctx, Base);
215  }
216  return Cl::CL_LValue;
217 
218  // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
219  // function or variable and a prvalue otherwise.
220  case Expr::DeclRefExprClass:
221  if (E->getType() == Ctx.UnknownAnyTy)
222  return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
224  return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
225 
226  // Member access is complex.
227  case Expr::MemberExprClass:
228  return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
229 
230  case Expr::UnaryOperatorClass:
231  switch (cast<UnaryOperator>(E)->getOpcode()) {
232  // C++ [expr.unary.op]p1: The unary * operator performs indirection:
233  // [...] the result is an lvalue referring to the object or function
234  // to which the expression points.
235  case UO_Deref:
236  return Cl::CL_LValue;
237 
238  // GNU extensions, simply look through them.
239  case UO_Extension:
240  return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
241 
242  // Treat _Real and _Imag basically as if they were member
243  // expressions: l-value only if the operand is a true l-value.
244  case UO_Real:
245  case UO_Imag: {
246  const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
247  Cl::Kinds K = ClassifyInternal(Ctx, Op);
248  if (K != Cl::CL_LValue) return K;
249 
250  if (isa<ObjCPropertyRefExpr>(Op))
252  return Cl::CL_LValue;
253  }
254 
255  // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
256  // lvalue, [...]
257  // Not so in C.
258  case UO_PreInc:
259  case UO_PreDec:
260  return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
261 
262  default:
263  return Cl::CL_PRValue;
264  }
265 
266  case Expr::OpaqueValueExprClass:
267  return ClassifyExprValueKind(Lang, E, E->getValueKind());
268 
269  // Pseudo-object expressions can produce l-values with reference magic.
270  case Expr::PseudoObjectExprClass:
271  return ClassifyExprValueKind(Lang, E,
272  cast<PseudoObjectExpr>(E)->getValueKind());
273 
274  // Implicit casts are lvalues if they're lvalue casts. Other than that, we
275  // only specifically record class temporaries.
276  case Expr::ImplicitCastExprClass:
277  return ClassifyExprValueKind(Lang, E, E->getValueKind());
278 
279  // C++ [expr.prim.general]p4: The presence of parentheses does not affect
280  // whether the expression is an lvalue.
281  case Expr::ParenExprClass:
282  return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
283 
284  // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
285  // or a void expression if its result expression is, respectively, an
286  // lvalue, a function designator, or a void expression.
287  case Expr::GenericSelectionExprClass:
288  if (cast<GenericSelectionExpr>(E)->isResultDependent())
289  return Cl::CL_PRValue;
290  return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
291 
292  case Expr::BinaryOperatorClass:
293  case Expr::CompoundAssignOperatorClass:
294  // C doesn't have any binary expressions that are lvalues.
295  if (Lang.CPlusPlus)
296  return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
297  return Cl::CL_PRValue;
298 
299  case Expr::CallExprClass:
300  case Expr::CXXOperatorCallExprClass:
301  case Expr::CXXMemberCallExprClass:
302  case Expr::UserDefinedLiteralClass:
303  case Expr::CUDAKernelCallExprClass:
304  return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
305 
306  // __builtin_choose_expr is equivalent to the chosen expression.
307  case Expr::ChooseExprClass:
308  return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
309 
310  // Extended vector element access is an lvalue unless there are duplicates
311  // in the shuffle expression.
312  case Expr::ExtVectorElementExprClass:
313  if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
315  if (cast<ExtVectorElementExpr>(E)->isArrow())
316  return Cl::CL_LValue;
317  return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
318 
319  // Simply look at the actual default argument.
320  case Expr::CXXDefaultArgExprClass:
321  return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
322 
323  // Same idea for default initializers.
324  case Expr::CXXDefaultInitExprClass:
325  return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
326 
327  // Same idea for temporary binding.
328  case Expr::CXXBindTemporaryExprClass:
329  return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
330 
331  // And the cleanups guard.
332  case Expr::ExprWithCleanupsClass:
333  return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
334 
335  // Casts depend completely on the target type. All casts work the same.
336  case Expr::CStyleCastExprClass:
337  case Expr::CXXFunctionalCastExprClass:
338  case Expr::CXXStaticCastExprClass:
339  case Expr::CXXDynamicCastExprClass:
340  case Expr::CXXReinterpretCastExprClass:
341  case Expr::CXXConstCastExprClass:
342  case Expr::ObjCBridgedCastExprClass:
343  // Only in C++ can casts be interesting at all.
344  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
345  return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
346 
347  case Expr::CXXUnresolvedConstructExprClass:
348  return ClassifyUnnamed(Ctx,
349  cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
350 
351  case Expr::BinaryConditionalOperatorClass: {
352  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
353  const auto *co = cast<BinaryConditionalOperator>(E);
354  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
355  }
356 
357  case Expr::ConditionalOperatorClass: {
358  // Once again, only C++ is interesting.
359  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
360  const auto *co = cast<ConditionalOperator>(E);
361  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
362  }
363 
364  // ObjC message sends are effectively function calls, if the target function
365  // is known.
366  case Expr::ObjCMessageExprClass:
367  if (const ObjCMethodDecl *Method =
368  cast<ObjCMessageExpr>(E)->getMethodDecl()) {
369  Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());
370  return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
371  }
372  return Cl::CL_PRValue;
373 
374  // Some C++ expressions are always class temporaries.
375  case Expr::CXXConstructExprClass:
376  case Expr::CXXInheritedCtorInitExprClass:
377  case Expr::CXXTemporaryObjectExprClass:
378  case Expr::LambdaExprClass:
379  case Expr::CXXStdInitializerListExprClass:
380  return Cl::CL_ClassTemporary;
381 
382  case Expr::VAArgExprClass:
383  return ClassifyUnnamed(Ctx, E->getType());
384 
385  case Expr::DesignatedInitExprClass:
386  return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
387 
388  case Expr::StmtExprClass: {
389  const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
390  if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
391  return ClassifyUnnamed(Ctx, LastExpr->getType());
392  return Cl::CL_PRValue;
393  }
394 
395  case Expr::CXXUuidofExprClass:
396  return Cl::CL_LValue;
397 
398  case Expr::PackExpansionExprClass:
399  return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
400 
401  case Expr::MaterializeTemporaryExprClass:
402  return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
403  ? Cl::CL_LValue
404  : Cl::CL_XValue;
405 
406  case Expr::InitListExprClass:
407  // An init list can be an lvalue if it is bound to a reference and
408  // contains only one element. In that case, we look at that element
409  // for an exact classification. Init list creation takes care of the
410  // value kind for us, so we only need to fine-tune.
411  if (E->isRValue())
412  return ClassifyExprValueKind(Lang, E, E->getValueKind());
413  assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
414  "Only 1-element init lists can be glvalues.");
415  return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
416 
417  case Expr::CoawaitExprClass:
418  case Expr::CoyieldExprClass:
419  return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr());
420  }
421 
422  llvm_unreachable("unhandled expression kind in classification");
423 }
424 
425 /// ClassifyDecl - Return the classification of an expression referencing the
426 /// given declaration.
427 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
428  // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
429  // function, variable, or data member and a prvalue otherwise.
430  // In C, functions are not lvalues.
431  // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
432  // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
433  // special-case this.
434 
435  if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
436  return Cl::CL_MemberFunction;
437 
438  bool islvalue;
439  if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))
440  islvalue = NTTParm->getType()->isReferenceType();
441  else
442  islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
443  isa<IndirectFieldDecl>(D) ||
444  isa<BindingDecl>(D) ||
445  (Ctx.getLangOpts().CPlusPlus &&
446  (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
447  isa<FunctionTemplateDecl>(D)));
448 
449  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
450 }
451 
452 /// ClassifyUnnamed - Return the classification of an expression yielding an
453 /// unnamed value of the given type. This applies in particular to function
454 /// calls and casts.
456  // In C, function calls are always rvalues.
457  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
458 
459  // C++ [expr.call]p10: A function call is an lvalue if the result type is an
460  // lvalue reference type or an rvalue reference to function type, an xvalue
461  // if the result type is an rvalue reference to object type, and a prvalue
462  // otherwise.
463  if (T->isLValueReferenceType())
464  return Cl::CL_LValue;
465  const auto *RV = T->getAs<RValueReferenceType>();
466  if (!RV) // Could still be a class temporary, though.
467  return ClassifyTemporary(T);
468 
469  return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
470 }
471 
473  if (E->getType() == Ctx.UnknownAnyTy)
474  return (isa<FunctionDecl>(E->getMemberDecl())
476 
477  // Handle C first, it's easier.
478  if (!Ctx.getLangOpts().CPlusPlus) {
479  // C99 6.5.2.3p3
480  // For dot access, the expression is an lvalue if the first part is. For
481  // arrow access, it always is an lvalue.
482  if (E->isArrow())
483  return Cl::CL_LValue;
484  // ObjC property accesses are not lvalues, but get special treatment.
485  Expr *Base = E->getBase()->IgnoreParens();
486  if (isa<ObjCPropertyRefExpr>(Base))
488  return ClassifyInternal(Ctx, Base);
489  }
490 
491  NamedDecl *Member = E->getMemberDecl();
492  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
493  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
494  // E1.E2 is an lvalue.
495  if (const auto *Value = dyn_cast<ValueDecl>(Member))
496  if (Value->getType()->isReferenceType())
497  return Cl::CL_LValue;
498 
499  // Otherwise, one of the following rules applies.
500  // -- If E2 is a static member [...] then E1.E2 is an lvalue.
501  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
502  return Cl::CL_LValue;
503 
504  // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
505  // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
506  // otherwise, it is a prvalue.
507  if (isa<FieldDecl>(Member)) {
508  // *E1 is an lvalue
509  if (E->isArrow())
510  return Cl::CL_LValue;
512  if (isa<ObjCPropertyRefExpr>(Base))
514  return ClassifyInternal(Ctx, E->getBase());
515  }
516 
517  // -- If E2 is a [...] member function, [...]
518  // -- If it refers to a static member function [...], then E1.E2 is an
519  // lvalue; [...]
520  // -- Otherwise [...] E1.E2 is a prvalue.
521  if (const auto *Method = dyn_cast<CXXMethodDecl>(Member))
522  return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
523 
524  // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
525  // So is everything else we haven't handled yet.
526  return Cl::CL_PRValue;
527 }
528 
530  assert(Ctx.getLangOpts().CPlusPlus &&
531  "This is only relevant for C++.");
532  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
533  // Except we override this for writes to ObjC properties.
534  if (E->isAssignmentOp())
535  return (E->getLHS()->getObjectKind() == OK_ObjCProperty
537 
538  // C++ [expr.comma]p1: the result is of the same value category as its right
539  // operand, [...].
540  if (E->getOpcode() == BO_Comma)
541  return ClassifyInternal(Ctx, E->getRHS());
542 
543  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
544  // is a pointer to a data member is of the same value category as its first
545  // operand.
546  if (E->getOpcode() == BO_PtrMemD)
547  return (E->getType()->isFunctionType() ||
548  E->hasPlaceholderType(BuiltinType::BoundMember))
550  : ClassifyInternal(Ctx, E->getLHS());
551 
552  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
553  // second operand is a pointer to data member and a prvalue otherwise.
554  if (E->getOpcode() == BO_PtrMemI)
555  return (E->getType()->isFunctionType() ||
556  E->hasPlaceholderType(BuiltinType::BoundMember))
558  : Cl::CL_LValue;
559 
560  // All other binary operations are prvalues.
561  return Cl::CL_PRValue;
562 }
563 
564 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
565  const Expr *False) {
566  assert(Ctx.getLangOpts().CPlusPlus &&
567  "This is only relevant for C++.");
568 
569  // C++ [expr.cond]p2
570  // If either the second or the third operand has type (cv) void,
571  // one of the following shall hold:
572  if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
573  // The second or the third operand (but not both) is a (possibly
574  // parenthesized) throw-expression; the result is of the [...] value
575  // category of the other.
576  bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
577  bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
578  if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
579  : (FalseIsThrow ? True : nullptr))
580  return ClassifyInternal(Ctx, NonThrow);
581 
582  // [Otherwise] the result [...] is a prvalue.
583  return Cl::CL_PRValue;
584  }
585 
586  // Note that at this point, we have already performed all conversions
587  // according to [expr.cond]p3.
588  // C++ [expr.cond]p4: If the second and third operands are glvalues of the
589  // same value category [...], the result is of that [...] value category.
590  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
591  Cl::Kinds LCl = ClassifyInternal(Ctx, True),
592  RCl = ClassifyInternal(Ctx, False);
593  return LCl == RCl ? LCl : Cl::CL_PRValue;
594 }
595 
597  Cl::Kinds Kind, SourceLocation &Loc) {
598  // As a general rule, we only care about lvalues. But there are some rvalues
599  // for which we want to generate special results.
600  if (Kind == Cl::CL_PRValue) {
601  // For the sake of better diagnostics, we want to specifically recognize
602  // use of the GCC cast-as-lvalue extension.
603  if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
604  if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
605  Loc = CE->getExprLoc();
606  return Cl::CM_LValueCast;
607  }
608  }
609  }
610  if (Kind != Cl::CL_LValue)
611  return Cl::CM_RValue;
612 
613  // This is the lvalue case.
614  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
615  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
616  return Cl::CM_Function;
617 
618  // Assignment to a property in ObjC is an implicit setter access. But a
619  // setter might not exist.
620  if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
621  if (Expr->isImplicitProperty() &&
622  Expr->getImplicitPropertySetter() == nullptr)
624  }
625 
626  CanQualType CT = Ctx.getCanonicalType(E->getType());
627  // Const stuff is obviously not modifiable.
628  if (CT.isConstQualified())
629  return Cl::CM_ConstQualified;
630  if (Ctx.getLangOpts().OpenCL &&
632  return Cl::CM_ConstAddrSpace;
633 
634  // Arrays are not modifiable, only their elements are.
635  if (CT->isArrayType())
636  return Cl::CM_ArrayType;
637  // Incomplete types are not modifiable.
638  if (CT->isIncompleteType())
639  return Cl::CM_IncompleteType;
640 
641  // Records with any const fields (recursively) are not modifiable.
642  if (const RecordType *R = CT->getAs<RecordType>())
643  if (R->hasConstFields())
645 
646  return Cl::CM_Modifiable;
647 }
648 
650  Classification VC = Classify(Ctx);
651  switch (VC.getKind()) {
652  case Cl::CL_LValue: return LV_Valid;
653  case Cl::CL_XValue: return LV_InvalidExpression;
654  case Cl::CL_Function: return LV_NotObjectType;
655  case Cl::CL_Void: return LV_InvalidExpression;
664  }
665  llvm_unreachable("Unhandled kind");
666 }
667 
670  SourceLocation dummy;
671  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
672  switch (VC.getKind()) {
673  case Cl::CL_LValue: break;
675  case Cl::CL_Function: return MLV_NotObjectType;
676  case Cl::CL_Void: return MLV_InvalidExpression;
684  case Cl::CL_PRValue:
685  return VC.getModifiable() == Cl::CM_LValueCast ?
687  }
688  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
689  switch (VC.getModifiable()) {
690  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
691  case Cl::CM_Modifiable: return MLV_Valid;
692  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
693  case Cl::CM_Function: return MLV_NotObjectType;
694  case Cl::CM_LValueCast:
695  llvm_unreachable("CM_LValueCast and CL_LValue don't match");
700  case Cl::CM_ArrayType: return MLV_ArrayType;
702  }
703  llvm_unreachable("Unhandled modifiable type");
704 }
Defines the clang::ASTContext interface.
Stmt * body_back()
Definition: Stmt.h:673
A (possibly-)qualified type.
Definition: Type.h:640
bool isArrayType() const
Definition: Type.h:6198
ValueDecl * getMemberDecl() const
Retrieve the member declaration to which this expression refers.
Definition: Expr.h:2692
bool isConstQualified() const
bool hasPlaceholderType() const
Returns whether this expression has a placeholder type.
Definition: Expr.h:472
bool isRecordType() const
Definition: Type.h:6222
Expr * getBase() const
Definition: Expr.h:2686
Decl - This represents one declaration (or definition), e.g.
Definition: DeclBase.h:86
Defines the C++ template declaration subclasses.
Opcode getOpcode() const
Definition: Expr.h:3304
Classification Classify(ASTContext &Ctx) const
Classify - Classify this expression according to the C++11 expression taxonomy.
Definition: Expr.h:377
isModifiableLvalueResult
Definition: Expr.h:269
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:6562
ObjCMethodDecl - Represents an instance or class method declaration.
Definition: DeclObjC.h:139
static bool isAssignmentOp(Opcode Opc)
Definition: Expr.h:3394
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:153
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:6161
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:389
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:50
An r-value expression (a pr-value in the C++11 taxonomy) produces a temporary value.
Definition: Specifiers.h:110
An rvalue reference type, per C++11 [dcl.ref].
Definition: Type.h:2642
An x-value expression is a reference to an object with independent storage but which can be "moved"...
Definition: Specifiers.h:119
ExprValueKind getValueKind() const
getValueKind - The value kind that this expression produces.
Definition: Expr.h:405
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:3263
LangAS getAddressSpace() const
Definition: Type.h:354
bool isArrow() const
Definition: Expr.h:2791
CompoundStmt - This represents a group of statements like { stmt stmt }.
Definition: Stmt.h:637
The return type of classify().
Definition: Expr.h:302
bool hasQualifiers() const
Determine whether this type has any qualifiers.
Definition: Type.h:6000
Kinds
The various classification results. Most of these mean prvalue.
Definition: Expr.h:305
An Objective-C property is a logical field of an Objective-C object which is read and written via Obj...
Definition: Specifiers.h:136
Expr - This represents one expression.
Definition: Expr.h:106
ExprValueKind
The categorization of expression values, currently following the C++11 scheme.
Definition: Specifiers.h:107
DeclContext * getDeclContext()
Definition: DeclBase.h:434
QualType getType() const
Definition: Expr.h:128
ModifiableType
The results of modification testing.
Definition: Expr.h:320
ExprObjectKind getObjectKind() const
getObjectKind - The object kind that this expression produces.
Definition: Expr.h:412
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:1052
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:249
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:3307
static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E)
Dataflow Directional Tag Classes.
ModifiableType getModifiable() const
Definition: Expr.h:348
bool isRecord() const
Definition: DeclBase.h:1844
BinaryOperator::Opcode getOpcode(const SymExpr *SE)
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:391
Kinds getKind() const
Definition: Expr.h:347
static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *trueExpr, const Expr *falseExpr)
Expr * IgnoreParenImpCasts() LLVM_READONLY
IgnoreParenImpCasts - Ignore parentheses and implicit casts.
Definition: Expr.cpp:2631
A helper class that allows the use of isa/cast/dyncast to detect TagType objects of structs/unions/cl...
Definition: Type.h:4183
CanQualType UnknownAnyTy
Definition: ASTContext.h:1052
bool isFunctionType() const
Definition: Type.h:6145
LValueClassification
Definition: Expr.h:254
CanQualType getCanonicalType(QualType T) const
Return the canonical (structural) type corresponding to the specified potentially non-canonical type ...
Definition: ASTContext.h:2257
bool isLValueReferenceType() const
Definition: Type.h:6165
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:2596
bool isVoidType() const
Definition: Type.h:6376
bool isRValue() const
Definition: Expr.h:250
unsigned kind
All of the diagnostics that can be emitted by the frontend.
Definition: DiagnosticIDs.h:61
static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E)
Expr * getRHS() const
Definition: Expr.h:3309
An l-value expression is a reference to an object with independent storage.
Definition: Specifiers.h:114
This represents a decl that may have a name.
Definition: Decl.h:248
const LangOptions & getLangOpts() const
Definition: ASTContext.h:715
Expr * IgnoreParens() LLVM_READONLY
IgnoreParens - Ignore parentheses.
Definition: Expr.cpp:2513