clang  9.0.0svn
ExprClassification.cpp
Go to the documentation of this file.
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  return Cl::CL_PRValue;
195 
196  case Expr::ConstantExprClass:
197  return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr());
198 
199  // Next come the complicated cases.
200  case Expr::SubstNonTypeTemplateParmExprClass:
201  return ClassifyInternal(Ctx,
202  cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
203 
204  // C, C++98 [expr.sub]p1: The result is an lvalue of type "T".
205  // C++11 (DR1213): in the case of an array operand, the result is an lvalue
206  // if that operand is an lvalue and an xvalue otherwise.
207  // Subscripting vector types is more like member access.
208  case Expr::ArraySubscriptExprClass:
209  if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
210  return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
211  if (Lang.CPlusPlus11) {
212  // Step over the array-to-pointer decay if present, but not over the
213  // temporary materialization.
214  auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts();
215  if (Base->getType()->isArrayType())
216  return ClassifyInternal(Ctx, Base);
217  }
218  return Cl::CL_LValue;
219 
220  // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
221  // function or variable and a prvalue otherwise.
222  case Expr::DeclRefExprClass:
223  if (E->getType() == Ctx.UnknownAnyTy)
224  return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
226  return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
227 
228  // Member access is complex.
229  case Expr::MemberExprClass:
230  return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
231 
232  case Expr::UnaryOperatorClass:
233  switch (cast<UnaryOperator>(E)->getOpcode()) {
234  // C++ [expr.unary.op]p1: The unary * operator performs indirection:
235  // [...] the result is an lvalue referring to the object or function
236  // to which the expression points.
237  case UO_Deref:
238  return Cl::CL_LValue;
239 
240  // GNU extensions, simply look through them.
241  case UO_Extension:
242  return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
243 
244  // Treat _Real and _Imag basically as if they were member
245  // expressions: l-value only if the operand is a true l-value.
246  case UO_Real:
247  case UO_Imag: {
248  const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
249  Cl::Kinds K = ClassifyInternal(Ctx, Op);
250  if (K != Cl::CL_LValue) return K;
251 
252  if (isa<ObjCPropertyRefExpr>(Op))
254  return Cl::CL_LValue;
255  }
256 
257  // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
258  // lvalue, [...]
259  // Not so in C.
260  case UO_PreInc:
261  case UO_PreDec:
262  return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
263 
264  default:
265  return Cl::CL_PRValue;
266  }
267 
268  case Expr::OpaqueValueExprClass:
269  return ClassifyExprValueKind(Lang, E, E->getValueKind());
270 
271  // Pseudo-object expressions can produce l-values with reference magic.
272  case Expr::PseudoObjectExprClass:
273  return ClassifyExprValueKind(Lang, E,
274  cast<PseudoObjectExpr>(E)->getValueKind());
275 
276  // Implicit casts are lvalues if they're lvalue casts. Other than that, we
277  // only specifically record class temporaries.
278  case Expr::ImplicitCastExprClass:
279  return ClassifyExprValueKind(Lang, E, E->getValueKind());
280 
281  // C++ [expr.prim.general]p4: The presence of parentheses does not affect
282  // whether the expression is an lvalue.
283  case Expr::ParenExprClass:
284  return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
285 
286  // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
287  // or a void expression if its result expression is, respectively, an
288  // lvalue, a function designator, or a void expression.
289  case Expr::GenericSelectionExprClass:
290  if (cast<GenericSelectionExpr>(E)->isResultDependent())
291  return Cl::CL_PRValue;
292  return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
293 
294  case Expr::BinaryOperatorClass:
295  case Expr::CompoundAssignOperatorClass:
296  // C doesn't have any binary expressions that are lvalues.
297  if (Lang.CPlusPlus)
298  return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
299  return Cl::CL_PRValue;
300 
301  case Expr::CallExprClass:
302  case Expr::CXXOperatorCallExprClass:
303  case Expr::CXXMemberCallExprClass:
304  case Expr::UserDefinedLiteralClass:
305  case Expr::CUDAKernelCallExprClass:
306  return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
307 
308  // __builtin_choose_expr is equivalent to the chosen expression.
309  case Expr::ChooseExprClass:
310  return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
311 
312  // Extended vector element access is an lvalue unless there are duplicates
313  // in the shuffle expression.
314  case Expr::ExtVectorElementExprClass:
315  if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
317  if (cast<ExtVectorElementExpr>(E)->isArrow())
318  return Cl::CL_LValue;
319  return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
320 
321  // Simply look at the actual default argument.
322  case Expr::CXXDefaultArgExprClass:
323  return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
324 
325  // Same idea for default initializers.
326  case Expr::CXXDefaultInitExprClass:
327  return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
328 
329  // Same idea for temporary binding.
330  case Expr::CXXBindTemporaryExprClass:
331  return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
332 
333  // And the cleanups guard.
334  case Expr::ExprWithCleanupsClass:
335  return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
336 
337  // Casts depend completely on the target type. All casts work the same.
338  case Expr::CStyleCastExprClass:
339  case Expr::CXXFunctionalCastExprClass:
340  case Expr::CXXStaticCastExprClass:
341  case Expr::CXXDynamicCastExprClass:
342  case Expr::CXXReinterpretCastExprClass:
343  case Expr::CXXConstCastExprClass:
344  case Expr::ObjCBridgedCastExprClass:
345  // Only in C++ can casts be interesting at all.
346  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
347  return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
348 
349  case Expr::CXXUnresolvedConstructExprClass:
350  return ClassifyUnnamed(Ctx,
351  cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
352 
353  case Expr::BinaryConditionalOperatorClass: {
354  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
355  const auto *co = cast<BinaryConditionalOperator>(E);
356  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
357  }
358 
359  case Expr::ConditionalOperatorClass: {
360  // Once again, only C++ is interesting.
361  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
362  const auto *co = cast<ConditionalOperator>(E);
363  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
364  }
365 
366  // ObjC message sends are effectively function calls, if the target function
367  // is known.
368  case Expr::ObjCMessageExprClass:
369  if (const ObjCMethodDecl *Method =
370  cast<ObjCMessageExpr>(E)->getMethodDecl()) {
371  Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());
372  return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
373  }
374  return Cl::CL_PRValue;
375 
376  // Some C++ expressions are always class temporaries.
377  case Expr::CXXConstructExprClass:
378  case Expr::CXXInheritedCtorInitExprClass:
379  case Expr::CXXTemporaryObjectExprClass:
380  case Expr::LambdaExprClass:
381  case Expr::CXXStdInitializerListExprClass:
382  return Cl::CL_ClassTemporary;
383 
384  case Expr::VAArgExprClass:
385  return ClassifyUnnamed(Ctx, E->getType());
386 
387  case Expr::DesignatedInitExprClass:
388  return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
389 
390  case Expr::StmtExprClass: {
391  const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
392  if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
393  return ClassifyUnnamed(Ctx, LastExpr->getType());
394  return Cl::CL_PRValue;
395  }
396 
397  case Expr::CXXUuidofExprClass:
398  return Cl::CL_LValue;
399 
400  case Expr::PackExpansionExprClass:
401  return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
402 
403  case Expr::MaterializeTemporaryExprClass:
404  return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
405  ? Cl::CL_LValue
406  : Cl::CL_XValue;
407 
408  case Expr::InitListExprClass:
409  // An init list can be an lvalue if it is bound to a reference and
410  // contains only one element. In that case, we look at that element
411  // for an exact classification. Init list creation takes care of the
412  // value kind for us, so we only need to fine-tune.
413  if (E->isRValue())
414  return ClassifyExprValueKind(Lang, E, E->getValueKind());
415  assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
416  "Only 1-element init lists can be glvalues.");
417  return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
418 
419  case Expr::CoawaitExprClass:
420  case Expr::CoyieldExprClass:
421  return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr());
422  }
423 
424  llvm_unreachable("unhandled expression kind in classification");
425 }
426 
427 /// ClassifyDecl - Return the classification of an expression referencing the
428 /// given declaration.
429 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
430  // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
431  // function, variable, or data member and a prvalue otherwise.
432  // In C, functions are not lvalues.
433  // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
434  // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
435  // special-case this.
436 
437  if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
438  return Cl::CL_MemberFunction;
439 
440  bool islvalue;
441  if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))
442  islvalue = NTTParm->getType()->isReferenceType();
443  else
444  islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
445  isa<IndirectFieldDecl>(D) ||
446  isa<BindingDecl>(D) ||
447  (Ctx.getLangOpts().CPlusPlus &&
448  (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
449  isa<FunctionTemplateDecl>(D)));
450 
451  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
452 }
453 
454 /// ClassifyUnnamed - Return the classification of an expression yielding an
455 /// unnamed value of the given type. This applies in particular to function
456 /// calls and casts.
458  // In C, function calls are always rvalues.
459  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
460 
461  // C++ [expr.call]p10: A function call is an lvalue if the result type is an
462  // lvalue reference type or an rvalue reference to function type, an xvalue
463  // if the result type is an rvalue reference to object type, and a prvalue
464  // otherwise.
465  if (T->isLValueReferenceType())
466  return Cl::CL_LValue;
467  const auto *RV = T->getAs<RValueReferenceType>();
468  if (!RV) // Could still be a class temporary, though.
469  return ClassifyTemporary(T);
470 
471  return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
472 }
473 
475  if (E->getType() == Ctx.UnknownAnyTy)
476  return (isa<FunctionDecl>(E->getMemberDecl())
478 
479  // Handle C first, it's easier.
480  if (!Ctx.getLangOpts().CPlusPlus) {
481  // C99 6.5.2.3p3
482  // For dot access, the expression is an lvalue if the first part is. For
483  // arrow access, it always is an lvalue.
484  if (E->isArrow())
485  return Cl::CL_LValue;
486  // ObjC property accesses are not lvalues, but get special treatment.
487  Expr *Base = E->getBase()->IgnoreParens();
488  if (isa<ObjCPropertyRefExpr>(Base))
490  return ClassifyInternal(Ctx, Base);
491  }
492 
493  NamedDecl *Member = E->getMemberDecl();
494  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
495  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
496  // E1.E2 is an lvalue.
497  if (const auto *Value = dyn_cast<ValueDecl>(Member))
498  if (Value->getType()->isReferenceType())
499  return Cl::CL_LValue;
500 
501  // Otherwise, one of the following rules applies.
502  // -- If E2 is a static member [...] then E1.E2 is an lvalue.
503  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
504  return Cl::CL_LValue;
505 
506  // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
507  // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
508  // otherwise, it is a prvalue.
509  if (isa<FieldDecl>(Member)) {
510  // *E1 is an lvalue
511  if (E->isArrow())
512  return Cl::CL_LValue;
514  if (isa<ObjCPropertyRefExpr>(Base))
516  return ClassifyInternal(Ctx, E->getBase());
517  }
518 
519  // -- If E2 is a [...] member function, [...]
520  // -- If it refers to a static member function [...], then E1.E2 is an
521  // lvalue; [...]
522  // -- Otherwise [...] E1.E2 is a prvalue.
523  if (const auto *Method = dyn_cast<CXXMethodDecl>(Member))
524  return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
525 
526  // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
527  // So is everything else we haven't handled yet.
528  return Cl::CL_PRValue;
529 }
530 
532  assert(Ctx.getLangOpts().CPlusPlus &&
533  "This is only relevant for C++.");
534  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
535  // Except we override this for writes to ObjC properties.
536  if (E->isAssignmentOp())
537  return (E->getLHS()->getObjectKind() == OK_ObjCProperty
539 
540  // C++ [expr.comma]p1: the result is of the same value category as its right
541  // operand, [...].
542  if (E->getOpcode() == BO_Comma)
543  return ClassifyInternal(Ctx, E->getRHS());
544 
545  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
546  // is a pointer to a data member is of the same value category as its first
547  // operand.
548  if (E->getOpcode() == BO_PtrMemD)
549  return (E->getType()->isFunctionType() ||
550  E->hasPlaceholderType(BuiltinType::BoundMember))
552  : ClassifyInternal(Ctx, E->getLHS());
553 
554  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
555  // second operand is a pointer to data member and a prvalue otherwise.
556  if (E->getOpcode() == BO_PtrMemI)
557  return (E->getType()->isFunctionType() ||
558  E->hasPlaceholderType(BuiltinType::BoundMember))
560  : Cl::CL_LValue;
561 
562  // All other binary operations are prvalues.
563  return Cl::CL_PRValue;
564 }
565 
566 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
567  const Expr *False) {
568  assert(Ctx.getLangOpts().CPlusPlus &&
569  "This is only relevant for C++.");
570 
571  // C++ [expr.cond]p2
572  // If either the second or the third operand has type (cv) void,
573  // one of the following shall hold:
574  if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
575  // The second or the third operand (but not both) is a (possibly
576  // parenthesized) throw-expression; the result is of the [...] value
577  // category of the other.
578  bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
579  bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
580  if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
581  : (FalseIsThrow ? True : nullptr))
582  return ClassifyInternal(Ctx, NonThrow);
583 
584  // [Otherwise] the result [...] is a prvalue.
585  return Cl::CL_PRValue;
586  }
587 
588  // Note that at this point, we have already performed all conversions
589  // according to [expr.cond]p3.
590  // C++ [expr.cond]p4: If the second and third operands are glvalues of the
591  // same value category [...], the result is of that [...] value category.
592  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
593  Cl::Kinds LCl = ClassifyInternal(Ctx, True),
594  RCl = ClassifyInternal(Ctx, False);
595  return LCl == RCl ? LCl : Cl::CL_PRValue;
596 }
597 
599  Cl::Kinds Kind, SourceLocation &Loc) {
600  // As a general rule, we only care about lvalues. But there are some rvalues
601  // for which we want to generate special results.
602  if (Kind == Cl::CL_PRValue) {
603  // For the sake of better diagnostics, we want to specifically recognize
604  // use of the GCC cast-as-lvalue extension.
605  if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
606  if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
607  Loc = CE->getExprLoc();
608  return Cl::CM_LValueCast;
609  }
610  }
611  }
612  if (Kind != Cl::CL_LValue)
613  return Cl::CM_RValue;
614 
615  // This is the lvalue case.
616  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
617  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
618  return Cl::CM_Function;
619 
620  // Assignment to a property in ObjC is an implicit setter access. But a
621  // setter might not exist.
622  if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
623  if (Expr->isImplicitProperty() &&
624  Expr->getImplicitPropertySetter() == nullptr)
626  }
627 
628  CanQualType CT = Ctx.getCanonicalType(E->getType());
629  // Const stuff is obviously not modifiable.
630  if (CT.isConstQualified())
631  return Cl::CM_ConstQualified;
632  if (Ctx.getLangOpts().OpenCL &&
634  return Cl::CM_ConstAddrSpace;
635 
636  // Arrays are not modifiable, only their elements are.
637  if (CT->isArrayType())
638  return Cl::CM_ArrayType;
639  // Incomplete types are not modifiable.
640  if (CT->isIncompleteType())
641  return Cl::CM_IncompleteType;
642 
643  // Records with any const fields (recursively) are not modifiable.
644  if (const RecordType *R = CT->getAs<RecordType>())
645  if (R->hasConstFields())
647 
648  return Cl::CM_Modifiable;
649 }
650 
652  Classification VC = Classify(Ctx);
653  switch (VC.getKind()) {
654  case Cl::CL_LValue: return LV_Valid;
655  case Cl::CL_XValue: return LV_InvalidExpression;
656  case Cl::CL_Function: return LV_NotObjectType;
657  case Cl::CL_Void: return LV_InvalidExpression;
666  }
667  llvm_unreachable("Unhandled kind");
668 }
669 
672  SourceLocation dummy;
673  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
674  switch (VC.getKind()) {
675  case Cl::CL_LValue: break;
677  case Cl::CL_Function: return MLV_NotObjectType;
678  case Cl::CL_Void: return MLV_InvalidExpression;
686  case Cl::CL_PRValue:
687  return VC.getModifiable() == Cl::CM_LValueCast ?
689  }
690  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
691  switch (VC.getModifiable()) {
692  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
693  case Cl::CM_Modifiable: return MLV_Valid;
694  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
695  case Cl::CM_Function: return MLV_NotObjectType;
696  case Cl::CM_LValueCast:
697  llvm_unreachable("CM_LValueCast and CL_LValue don't match");
702  case Cl::CM_ArrayType: return MLV_ArrayType;
704  }
705  llvm_unreachable("Unhandled modifiable type");
706 }
Defines the clang::ASTContext interface.
Stmt * body_back()
Definition: Stmt.h:1275
A (possibly-)qualified type.
Definition: Type.h:634
bool isArrayType() const
Definition: Type.h:6350
ValueDecl * getMemberDecl() const
Retrieve the member declaration to which this expression refers.
Definition: Expr.h:2811
bool isConstQualified() const
bool hasPlaceholderType() const
Returns whether this expression has a placeholder type.
Definition: Expr.h:474
bool isRecordType() const
Definition: Type.h:6374
Expr * getBase() const
Definition: Expr.h:2805
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:3348
Classification Classify(ASTContext &Ctx) const
Classify - Classify this expression according to the C++11 expression taxonomy.
Definition: Expr.h:379
isModifiableLvalueResult
Definition: Expr.h:271
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:6761
ObjCMethodDecl - Represents an instance or class method declaration.
Definition: DeclObjC.h:138
static bool isAssignmentOp(Opcode Opc)
Definition: Expr.h:3436
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:154
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:6313
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:391
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:109
An rvalue reference type, per C++11 [dcl.ref].
Definition: Type.h:2743
An x-value expression is a reference to an object with independent storage but which can be "moved"...
Definition: Specifiers.h:118
ExprValueKind getValueKind() const
getValueKind - The value kind that this expression produces.
Definition: Expr.h:407
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:3313
LangAS getAddressSpace() const
Definition: Type.h:348
bool isArrow() const
Definition: Expr.h:2912
CompoundStmt - This represents a group of statements like { stmt stmt }.
Definition: Stmt.h:1237
The return type of classify().
Definition: Expr.h:304
bool hasQualifiers() const
Determine whether this type has any qualifiers.
Definition: Type.h:6152
Kinds
The various classification results. Most of these mean prvalue.
Definition: Expr.h:307
An Objective-C property is a logical field of an Objective-C object which is read and written via Obj...
Definition: Specifiers.h:135
This represents one expression.
Definition: Expr.h:108
ExprValueKind
The categorization of expression values, currently following the C++11 scheme.
Definition: Specifiers.h:106
DeclContext * getDeclContext()
Definition: DeclBase.h:429
QualType getType() const
Definition: Expr.h:130
ModifiableType
The results of modification testing.
Definition: Expr.h:322
ExprObjectKind getObjectKind() const
getObjectKind - The object kind that this expression produces.
Definition: Expr.h:414
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:251
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:3353
static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E)
Dataflow Directional Tag Classes.
ModifiableType getModifiable() const
Definition: Expr.h:350
bool isRecord() const
Definition: DeclBase.h:1830
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:1032
Kinds getKind() const
Definition: Expr.h:349
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:2720
A helper class that allows the use of isa/cast/dyncast to detect TagType objects of structs/unions/cl...
Definition: Type.h:4375
CanQualType UnknownAnyTy
Definition: ASTContext.h:1044
bool isFunctionType() const
Definition: Type.h:6297
LValueClassification
Definition: Expr.h:256
CanQualType getCanonicalType(QualType T) const
Return the canonical (structural) type corresponding to the specified potentially non-canonical type ...
Definition: ASTContext.h:2266
bool isLValueReferenceType() const
Definition: Type.h:6317
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:2720
bool isVoidType() const
Definition: Type.h:6553
bool isRValue() const
Definition: Expr.h:252
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:3355
An l-value expression is a reference to an object with independent storage.
Definition: Specifiers.h:113
This represents a decl that may have a name.
Definition: Decl.h:248
const LangOptions & getLangOpts() const
Definition: ASTContext.h:706
Expr * IgnoreParens() LLVM_READONLY
Skip past any parentheses which might surround this expression until reaching a fixed point...
Definition: Expr.cpp:2593