clang  11.0.0git
ExprClassification.cpp
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1 //===- ExprClassification.cpp - Expression AST Node Implementation --------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements Expr::classify.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "clang/AST/Expr.h"
14 #include "clang/AST/ASTContext.h"
15 #include "clang/AST/DeclCXX.h"
16 #include "clang/AST/DeclObjC.h"
17 #include "clang/AST/DeclTemplate.h"
18 #include "clang/AST/ExprCXX.h"
19 #include "clang/AST/ExprObjC.h"
20 #include "llvm/Support/ErrorHandling.h"
21 
22 using namespace clang;
23 
25 
26 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E);
27 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D);
29 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E);
32  const Expr *trueExpr,
33  const Expr *falseExpr);
34 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
36 
37 Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {
38  assert(!TR->isReferenceType() && "Expressions can't have reference type.");
39 
40  Cl::Kinds kind = ClassifyInternal(Ctx, this);
41  // C99 6.3.2.1: An lvalue is an expression with an object type or an
42  // incomplete type other than void.
43  if (!Ctx.getLangOpts().CPlusPlus) {
44  // Thus, no functions.
45  if (TR->isFunctionType() || TR == Ctx.OverloadTy)
46  kind = Cl::CL_Function;
47  // No void either, but qualified void is OK because it is "other than void".
48  // Void "lvalues" are classified as addressable void values, which are void
49  // expressions whose address can be taken.
50  else if (TR->isVoidType() && !TR.hasQualifiers())
52  }
53 
54  // Enable this assertion for testing.
55  switch (kind) {
56  case Cl::CL_LValue: assert(getValueKind() == VK_LValue); break;
57  case Cl::CL_XValue: assert(getValueKind() == VK_XValue); break;
58  case Cl::CL_Function:
59  case Cl::CL_Void:
67  case Cl::CL_PRValue: assert(getValueKind() == VK_RValue); break;
68  }
69 
71  if (Loc)
72  modifiable = IsModifiable(Ctx, this, kind, *Loc);
73  return Classification(kind, modifiable);
74 }
75 
76 /// Classify an expression which creates a temporary, based on its type.
78  if (T->isRecordType())
79  return Cl::CL_ClassTemporary;
80  if (T->isArrayType())
81  return Cl::CL_ArrayTemporary;
82 
83  // No special classification: these don't behave differently from normal
84  // prvalues.
85  return Cl::CL_PRValue;
86 }
87 
89  const Expr *E,
91  switch (Kind) {
92  case VK_RValue:
93  return Lang.CPlusPlus ? ClassifyTemporary(E->getType()) : Cl::CL_PRValue;
94  case VK_LValue:
95  return Cl::CL_LValue;
96  case VK_XValue:
97  return Cl::CL_XValue;
98  }
99  llvm_unreachable("Invalid value category of implicit cast.");
100 }
101 
102 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
103  // This function takes the first stab at classifying expressions.
104  const LangOptions &Lang = Ctx.getLangOpts();
105 
106  switch (E->getStmtClass()) {
107  case Stmt::NoStmtClass:
108 #define ABSTRACT_STMT(Kind)
109 #define STMT(Kind, Base) case Expr::Kind##Class:
110 #define EXPR(Kind, Base)
111 #include "clang/AST/StmtNodes.inc"
112  llvm_unreachable("cannot classify a statement");
113 
114  // First come the expressions that are always lvalues, unconditionally.
115  case Expr::ObjCIsaExprClass:
116  // C++ [expr.prim.general]p1: A string literal is an lvalue.
117  case Expr::StringLiteralClass:
118  // @encode is equivalent to its string
119  case Expr::ObjCEncodeExprClass:
120  // __func__ and friends are too.
121  case Expr::PredefinedExprClass:
122  // Property references are lvalues
123  case Expr::ObjCSubscriptRefExprClass:
124  case Expr::ObjCPropertyRefExprClass:
125  // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...
126  case Expr::CXXTypeidExprClass:
127  case Expr::CXXUuidofExprClass:
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::RecoveryExprClass:
134  case Expr::DependentCoawaitExprClass:
135  case Expr::CXXDependentScopeMemberExprClass:
136  case Expr::DependentScopeDeclRefExprClass:
137  // ObjC instance variables are lvalues
138  // FIXME: ObjC++0x might have different rules
139  case Expr::ObjCIvarRefExprClass:
140  case Expr::FunctionParmPackExprClass:
141  case Expr::MSPropertyRefExprClass:
142  case Expr::MSPropertySubscriptExprClass:
143  case Expr::OMPArraySectionExprClass:
144  case Expr::OMPArrayShapingExprClass:
145  case Expr::OMPIteratorExprClass:
146  return Cl::CL_LValue;
147 
148  // C99 6.5.2.5p5 says that compound literals are lvalues.
149  // In C++, they're prvalue temporaries, except for file-scope arrays.
150  case Expr::CompoundLiteralExprClass:
151  return !E->isLValue() ? ClassifyTemporary(E->getType()) : Cl::CL_LValue;
152 
153  // Expressions that are prvalues.
154  case Expr::CXXBoolLiteralExprClass:
155  case Expr::CXXPseudoDestructorExprClass:
156  case Expr::UnaryExprOrTypeTraitExprClass:
157  case Expr::CXXNewExprClass:
158  case Expr::CXXThisExprClass:
159  case Expr::CXXNullPtrLiteralExprClass:
160  case Expr::ImaginaryLiteralClass:
161  case Expr::GNUNullExprClass:
162  case Expr::OffsetOfExprClass:
163  case Expr::CXXThrowExprClass:
164  case Expr::ShuffleVectorExprClass:
165  case Expr::ConvertVectorExprClass:
166  case Expr::IntegerLiteralClass:
167  case Expr::FixedPointLiteralClass:
168  case Expr::CharacterLiteralClass:
169  case Expr::AddrLabelExprClass:
170  case Expr::CXXDeleteExprClass:
171  case Expr::ImplicitValueInitExprClass:
172  case Expr::BlockExprClass:
173  case Expr::FloatingLiteralClass:
174  case Expr::CXXNoexceptExprClass:
175  case Expr::CXXScalarValueInitExprClass:
176  case Expr::TypeTraitExprClass:
177  case Expr::ArrayTypeTraitExprClass:
178  case Expr::ExpressionTraitExprClass:
179  case Expr::ObjCSelectorExprClass:
180  case Expr::ObjCProtocolExprClass:
181  case Expr::ObjCStringLiteralClass:
182  case Expr::ObjCBoxedExprClass:
183  case Expr::ObjCArrayLiteralClass:
184  case Expr::ObjCDictionaryLiteralClass:
185  case Expr::ObjCBoolLiteralExprClass:
186  case Expr::ObjCAvailabilityCheckExprClass:
187  case Expr::ParenListExprClass:
188  case Expr::SizeOfPackExprClass:
189  case Expr::SubstNonTypeTemplateParmPackExprClass:
190  case Expr::AsTypeExprClass:
191  case Expr::ObjCIndirectCopyRestoreExprClass:
192  case Expr::AtomicExprClass:
193  case Expr::CXXFoldExprClass:
194  case Expr::ArrayInitLoopExprClass:
195  case Expr::ArrayInitIndexExprClass:
196  case Expr::NoInitExprClass:
197  case Expr::DesignatedInitUpdateExprClass:
198  case Expr::SourceLocExprClass:
199  case Expr::ConceptSpecializationExprClass:
200  case Expr::RequiresExprClass:
201  return Cl::CL_PRValue;
202 
203  case Expr::ConstantExprClass:
204  return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr());
205 
206  // Next come the complicated cases.
207  case Expr::SubstNonTypeTemplateParmExprClass:
208  return ClassifyInternal(Ctx,
209  cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
210 
211  // C, C++98 [expr.sub]p1: The result is an lvalue of type "T".
212  // C++11 (DR1213): in the case of an array operand, the result is an lvalue
213  // if that operand is an lvalue and an xvalue otherwise.
214  // Subscripting vector types is more like member access.
215  case Expr::ArraySubscriptExprClass:
216  if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
217  return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
218  if (Lang.CPlusPlus11) {
219  // Step over the array-to-pointer decay if present, but not over the
220  // temporary materialization.
221  auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts();
222  if (Base->getType()->isArrayType())
223  return ClassifyInternal(Ctx, Base);
224  }
225  return Cl::CL_LValue;
226 
227  // Subscripting matrix types behaves like member accesses.
228  case Expr::MatrixSubscriptExprClass:
229  return ClassifyInternal(Ctx, cast<MatrixSubscriptExpr>(E)->getBase());
230 
231  // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
232  // function or variable and a prvalue otherwise.
233  case Expr::DeclRefExprClass:
234  if (E->getType() == Ctx.UnknownAnyTy)
235  return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
237  return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
238 
239  // Member access is complex.
240  case Expr::MemberExprClass:
241  return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
242 
243  case Expr::UnaryOperatorClass:
244  switch (cast<UnaryOperator>(E)->getOpcode()) {
245  // C++ [expr.unary.op]p1: The unary * operator performs indirection:
246  // [...] the result is an lvalue referring to the object or function
247  // to which the expression points.
248  case UO_Deref:
249  return Cl::CL_LValue;
250 
251  // GNU extensions, simply look through them.
252  case UO_Extension:
253  return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
254 
255  // Treat _Real and _Imag basically as if they were member
256  // expressions: l-value only if the operand is a true l-value.
257  case UO_Real:
258  case UO_Imag: {
259  const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
260  Cl::Kinds K = ClassifyInternal(Ctx, Op);
261  if (K != Cl::CL_LValue) return K;
262 
263  if (isa<ObjCPropertyRefExpr>(Op))
265  return Cl::CL_LValue;
266  }
267 
268  // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
269  // lvalue, [...]
270  // Not so in C.
271  case UO_PreInc:
272  case UO_PreDec:
273  return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
274 
275  default:
276  return Cl::CL_PRValue;
277  }
278 
279  case Expr::OpaqueValueExprClass:
280  return ClassifyExprValueKind(Lang, E, E->getValueKind());
281 
282  // Pseudo-object expressions can produce l-values with reference magic.
283  case Expr::PseudoObjectExprClass:
284  return ClassifyExprValueKind(Lang, E,
285  cast<PseudoObjectExpr>(E)->getValueKind());
286 
287  // Implicit casts are lvalues if they're lvalue casts. Other than that, we
288  // only specifically record class temporaries.
289  case Expr::ImplicitCastExprClass:
290  return ClassifyExprValueKind(Lang, E, E->getValueKind());
291 
292  // C++ [expr.prim.general]p4: The presence of parentheses does not affect
293  // whether the expression is an lvalue.
294  case Expr::ParenExprClass:
295  return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
296 
297  // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
298  // or a void expression if its result expression is, respectively, an
299  // lvalue, a function designator, or a void expression.
300  case Expr::GenericSelectionExprClass:
301  if (cast<GenericSelectionExpr>(E)->isResultDependent())
302  return Cl::CL_PRValue;
303  return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
304 
305  case Expr::BinaryOperatorClass:
306  case Expr::CompoundAssignOperatorClass:
307  // C doesn't have any binary expressions that are lvalues.
308  if (Lang.CPlusPlus)
309  return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
310  return Cl::CL_PRValue;
311 
312  case Expr::CallExprClass:
313  case Expr::CXXOperatorCallExprClass:
314  case Expr::CXXMemberCallExprClass:
315  case Expr::UserDefinedLiteralClass:
316  case Expr::CUDAKernelCallExprClass:
317  return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
318 
319  case Expr::CXXRewrittenBinaryOperatorClass:
320  return ClassifyInternal(
321  Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm());
322 
323  // __builtin_choose_expr is equivalent to the chosen expression.
324  case Expr::ChooseExprClass:
325  return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
326 
327  // Extended vector element access is an lvalue unless there are duplicates
328  // in the shuffle expression.
329  case Expr::ExtVectorElementExprClass:
330  if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
332  if (cast<ExtVectorElementExpr>(E)->isArrow())
333  return Cl::CL_LValue;
334  return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
335 
336  // Simply look at the actual default argument.
337  case Expr::CXXDefaultArgExprClass:
338  return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
339 
340  // Same idea for default initializers.
341  case Expr::CXXDefaultInitExprClass:
342  return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
343 
344  // Same idea for temporary binding.
345  case Expr::CXXBindTemporaryExprClass:
346  return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
347 
348  // And the cleanups guard.
349  case Expr::ExprWithCleanupsClass:
350  return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
351 
352  // Casts depend completely on the target type. All casts work the same.
353  case Expr::CStyleCastExprClass:
354  case Expr::CXXFunctionalCastExprClass:
355  case Expr::CXXStaticCastExprClass:
356  case Expr::CXXDynamicCastExprClass:
357  case Expr::CXXReinterpretCastExprClass:
358  case Expr::CXXConstCastExprClass:
359  case Expr::CXXAddrspaceCastExprClass:
360  case Expr::ObjCBridgedCastExprClass:
361  case Expr::BuiltinBitCastExprClass:
362  // Only in C++ can casts be interesting at all.
363  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
364  return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
365 
366  case Expr::CXXUnresolvedConstructExprClass:
367  return ClassifyUnnamed(Ctx,
368  cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
369 
370  case Expr::BinaryConditionalOperatorClass: {
371  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
372  const auto *co = cast<BinaryConditionalOperator>(E);
373  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
374  }
375 
376  case Expr::ConditionalOperatorClass: {
377  // Once again, only C++ is interesting.
378  if (!Lang.CPlusPlus) return Cl::CL_PRValue;
379  const auto *co = cast<ConditionalOperator>(E);
380  return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
381  }
382 
383  // ObjC message sends are effectively function calls, if the target function
384  // is known.
385  case Expr::ObjCMessageExprClass:
386  if (const ObjCMethodDecl *Method =
387  cast<ObjCMessageExpr>(E)->getMethodDecl()) {
388  Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());
389  return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
390  }
391  return Cl::CL_PRValue;
392 
393  // Some C++ expressions are always class temporaries.
394  case Expr::CXXConstructExprClass:
395  case Expr::CXXInheritedCtorInitExprClass:
396  case Expr::CXXTemporaryObjectExprClass:
397  case Expr::LambdaExprClass:
398  case Expr::CXXStdInitializerListExprClass:
399  return Cl::CL_ClassTemporary;
400 
401  case Expr::VAArgExprClass:
402  return ClassifyUnnamed(Ctx, E->getType());
403 
404  case Expr::DesignatedInitExprClass:
405  return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
406 
407  case Expr::StmtExprClass: {
408  const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
409  if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
410  return ClassifyUnnamed(Ctx, LastExpr->getType());
411  return Cl::CL_PRValue;
412  }
413 
414  case Expr::PackExpansionExprClass:
415  return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
416 
417  case Expr::MaterializeTemporaryExprClass:
418  return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
419  ? Cl::CL_LValue
420  : Cl::CL_XValue;
421 
422  case Expr::InitListExprClass:
423  // An init list can be an lvalue if it is bound to a reference and
424  // contains only one element. In that case, we look at that element
425  // for an exact classification. Init list creation takes care of the
426  // value kind for us, so we only need to fine-tune.
427  if (E->isRValue())
428  return ClassifyExprValueKind(Lang, E, E->getValueKind());
429  assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
430  "Only 1-element init lists can be glvalues.");
431  return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
432 
433  case Expr::CoawaitExprClass:
434  case Expr::CoyieldExprClass:
435  return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr());
436  }
437 
438  llvm_unreachable("unhandled expression kind in classification");
439 }
440 
441 /// ClassifyDecl - Return the classification of an expression referencing the
442 /// given declaration.
443 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
444  // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
445  // function, variable, or data member and a prvalue otherwise.
446  // In C, functions are not lvalues.
447  // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
448  // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
449  // special-case this.
450 
451  if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
452  return Cl::CL_MemberFunction;
453 
454  bool islvalue;
455  if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))
456  islvalue = NTTParm->getType()->isReferenceType();
457  else
458  islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
459  isa<IndirectFieldDecl>(D) ||
460  isa<BindingDecl>(D) ||
461  isa<MSGuidDecl>(D) ||
462  (Ctx.getLangOpts().CPlusPlus &&
463  (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
464  isa<FunctionTemplateDecl>(D)));
465 
466  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
467 }
468 
469 /// ClassifyUnnamed - Return the classification of an expression yielding an
470 /// unnamed value of the given type. This applies in particular to function
471 /// calls and casts.
473  // In C, function calls are always rvalues.
474  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
475 
476  // C++ [expr.call]p10: A function call is an lvalue if the result type is an
477  // lvalue reference type or an rvalue reference to function type, an xvalue
478  // if the result type is an rvalue reference to object type, and a prvalue
479  // otherwise.
480  if (T->isLValueReferenceType())
481  return Cl::CL_LValue;
482  const auto *RV = T->getAs<RValueReferenceType>();
483  if (!RV) // Could still be a class temporary, though.
484  return ClassifyTemporary(T);
485 
486  return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
487 }
488 
490  if (E->getType() == Ctx.UnknownAnyTy)
491  return (isa<FunctionDecl>(E->getMemberDecl())
493 
494  // Handle C first, it's easier.
495  if (!Ctx.getLangOpts().CPlusPlus) {
496  // C99 6.5.2.3p3
497  // For dot access, the expression is an lvalue if the first part is. For
498  // arrow access, it always is an lvalue.
499  if (E->isArrow())
500  return Cl::CL_LValue;
501  // ObjC property accesses are not lvalues, but get special treatment.
502  Expr *Base = E->getBase()->IgnoreParens();
503  if (isa<ObjCPropertyRefExpr>(Base))
505  return ClassifyInternal(Ctx, Base);
506  }
507 
508  NamedDecl *Member = E->getMemberDecl();
509  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
510  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
511  // E1.E2 is an lvalue.
512  if (const auto *Value = dyn_cast<ValueDecl>(Member))
513  if (Value->getType()->isReferenceType())
514  return Cl::CL_LValue;
515 
516  // Otherwise, one of the following rules applies.
517  // -- If E2 is a static member [...] then E1.E2 is an lvalue.
518  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
519  return Cl::CL_LValue;
520 
521  // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
522  // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
523  // otherwise, it is a prvalue.
524  if (isa<FieldDecl>(Member)) {
525  // *E1 is an lvalue
526  if (E->isArrow())
527  return Cl::CL_LValue;
529  if (isa<ObjCPropertyRefExpr>(Base))
531  return ClassifyInternal(Ctx, E->getBase());
532  }
533 
534  // -- If E2 is a [...] member function, [...]
535  // -- If it refers to a static member function [...], then E1.E2 is an
536  // lvalue; [...]
537  // -- Otherwise [...] E1.E2 is a prvalue.
538  if (const auto *Method = dyn_cast<CXXMethodDecl>(Member))
539  return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
540 
541  // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
542  // So is everything else we haven't handled yet.
543  return Cl::CL_PRValue;
544 }
545 
547  assert(Ctx.getLangOpts().CPlusPlus &&
548  "This is only relevant for C++.");
549  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
550  // Except we override this for writes to ObjC properties.
551  if (E->isAssignmentOp())
552  return (E->getLHS()->getObjectKind() == OK_ObjCProperty
554 
555  // C++ [expr.comma]p1: the result is of the same value category as its right
556  // operand, [...].
557  if (E->getOpcode() == BO_Comma)
558  return ClassifyInternal(Ctx, E->getRHS());
559 
560  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
561  // is a pointer to a data member is of the same value category as its first
562  // operand.
563  if (E->getOpcode() == BO_PtrMemD)
564  return (E->getType()->isFunctionType() ||
565  E->hasPlaceholderType(BuiltinType::BoundMember))
567  : ClassifyInternal(Ctx, E->getLHS());
568 
569  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
570  // second operand is a pointer to data member and a prvalue otherwise.
571  if (E->getOpcode() == BO_PtrMemI)
572  return (E->getType()->isFunctionType() ||
573  E->hasPlaceholderType(BuiltinType::BoundMember))
575  : Cl::CL_LValue;
576 
577  // All other binary operations are prvalues.
578  return Cl::CL_PRValue;
579 }
580 
581 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
582  const Expr *False) {
583  assert(Ctx.getLangOpts().CPlusPlus &&
584  "This is only relevant for C++.");
585 
586  // C++ [expr.cond]p2
587  // If either the second or the third operand has type (cv) void,
588  // one of the following shall hold:
589  if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
590  // The second or the third operand (but not both) is a (possibly
591  // parenthesized) throw-expression; the result is of the [...] value
592  // category of the other.
593  bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
594  bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
595  if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
596  : (FalseIsThrow ? True : nullptr))
597  return ClassifyInternal(Ctx, NonThrow);
598 
599  // [Otherwise] the result [...] is a prvalue.
600  return Cl::CL_PRValue;
601  }
602 
603  // Note that at this point, we have already performed all conversions
604  // according to [expr.cond]p3.
605  // C++ [expr.cond]p4: If the second and third operands are glvalues of the
606  // same value category [...], the result is of that [...] value category.
607  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
608  Cl::Kinds LCl = ClassifyInternal(Ctx, True),
609  RCl = ClassifyInternal(Ctx, False);
610  return LCl == RCl ? LCl : Cl::CL_PRValue;
611 }
612 
614  Cl::Kinds Kind, SourceLocation &Loc) {
615  // As a general rule, we only care about lvalues. But there are some rvalues
616  // for which we want to generate special results.
617  if (Kind == Cl::CL_PRValue) {
618  // For the sake of better diagnostics, we want to specifically recognize
619  // use of the GCC cast-as-lvalue extension.
620  if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
621  if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
622  Loc = CE->getExprLoc();
623  return Cl::CM_LValueCast;
624  }
625  }
626  }
627  if (Kind != Cl::CL_LValue)
628  return Cl::CM_RValue;
629 
630  // This is the lvalue case.
631  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
632  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
633  return Cl::CM_Function;
634 
635  // Assignment to a property in ObjC is an implicit setter access. But a
636  // setter might not exist.
637  if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
638  if (Expr->isImplicitProperty() &&
639  Expr->getImplicitPropertySetter() == nullptr)
641  }
642 
643  CanQualType CT = Ctx.getCanonicalType(E->getType());
644  // Const stuff is obviously not modifiable.
645  if (CT.isConstQualified())
646  return Cl::CM_ConstQualified;
647  if (Ctx.getLangOpts().OpenCL &&
649  return Cl::CM_ConstAddrSpace;
650 
651  // Arrays are not modifiable, only their elements are.
652  if (CT->isArrayType())
653  return Cl::CM_ArrayType;
654  // Incomplete types are not modifiable.
655  if (CT->isIncompleteType())
656  return Cl::CM_IncompleteType;
657 
658  // Records with any const fields (recursively) are not modifiable.
659  if (const RecordType *R = CT->getAs<RecordType>())
660  if (R->hasConstFields())
662 
663  return Cl::CM_Modifiable;
664 }
665 
667  Classification VC = Classify(Ctx);
668  switch (VC.getKind()) {
669  case Cl::CL_LValue: return LV_Valid;
670  case Cl::CL_XValue: return LV_InvalidExpression;
671  case Cl::CL_Function: return LV_NotObjectType;
672  case Cl::CL_Void: return LV_InvalidExpression;
681  }
682  llvm_unreachable("Unhandled kind");
683 }
684 
687  SourceLocation dummy;
688  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
689  switch (VC.getKind()) {
690  case Cl::CL_LValue: break;
692  case Cl::CL_Function: return MLV_NotObjectType;
693  case Cl::CL_Void: return MLV_InvalidExpression;
701  case Cl::CL_PRValue:
702  return VC.getModifiable() == Cl::CM_LValueCast ?
704  }
705  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
706  switch (VC.getModifiable()) {
707  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
708  case Cl::CM_Modifiable: return MLV_Valid;
709  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
710  case Cl::CM_Function: return MLV_NotObjectType;
711  case Cl::CM_LValueCast:
712  llvm_unreachable("CM_LValueCast and CL_LValue don't match");
717  case Cl::CM_ArrayType: return MLV_ArrayType;
719  }
720  llvm_unreachable("Unhandled modifiable type");
721 }
Defines the clang::ASTContext interface.
Stmt * body_back()
Definition: Stmt.h:1402
A (possibly-)qualified type.
Definition: Type.h:655
bool isArrayType() const
Definition: Type.h:6716
ValueDecl * getMemberDecl() const
Retrieve the member declaration to which this expression refers.
Definition: Expr.h:3133
bool isConstQualified() const
bool hasPlaceholderType() const
Returns whether this expression has a placeholder type.
Definition: Expr.h:489
bool isRecordType() const
Definition: Type.h:6740
Expr * getBase() const
Definition: Expr.h:3127
Decl - This represents one declaration (or definition), e.g.
Definition: DeclBase.h:89
Defines the C++ template declaration subclasses.
Opcode getOpcode() const
Definition: Expr.h:3676
Classification Classify(ASTContext &Ctx) const
Classify - Classify this expression according to the C++11 expression taxonomy.
Definition: Expr.h:389
isModifiableLvalueResult
Definition: Expr.h:281
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:7153
ObjCMethodDecl - Represents an instance or class method declaration.
Definition: DeclObjC.h:139
static bool isAssignmentOp(Opcode Opc)
Definition: Expr.h:3767
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:174
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:6662
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:401
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:54
An r-value expression (a pr-value in the C++11 taxonomy) produces a temporary value.
Definition: Specifiers.h:127
An rvalue reference type, per C++11 [dcl.ref].
Definition: Type.h:2818
An x-value expression is a reference to an object with independent storage but which can be "moved"...
Definition: Specifiers.h:136
ExprValueKind getValueKind() const
getValueKind - The value kind that this expression produces.
Definition: Expr.h:417
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:3632
LangAS getAddressSpace() const
Definition: Type.h:360
bool isArrow() const
Definition: Expr.h:3234
CompoundStmt - This represents a group of statements like { stmt stmt }.
Definition: Stmt.h:1364
The return type of classify().
Definition: Expr.h:314
bool hasQualifiers() const
Determine whether this type has any qualifiers.
Definition: Type.h:6477
Kinds
The various classification results. Most of these mean prvalue.
Definition: Expr.h:317
An Objective-C property is a logical field of an Objective-C object which is read and written via Obj...
Definition: Specifiers.h:153
This represents one expression.
Definition: Expr.h:110
ExprValueKind
The categorization of expression values, currently following the C++11 scheme.
Definition: Specifiers.h:124
DeclContext * getDeclContext()
Definition: DeclBase.h:439
QualType getType() const
Definition: Expr.h:142
ModifiableType
The results of modification testing.
Definition: Expr.h:332
ExprObjectKind getObjectKind() const
getObjectKind - The object kind that this expression produces.
Definition: Expr.h:424
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:972
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:261
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:3681
static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E)
Dataflow Directional Tag Classes.
ModifiableType getModifiable() const
Definition: Expr.h:360
bool isRecord() const
Definition: DeclBase.h:1891
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:1148
Kinds getKind() const
Definition: Expr.h:359
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:2947
A helper class that allows the use of isa/cast/dyncast to detect TagType objects of structs/unions/cl...
Definition: Type.h:4617
CanQualType UnknownAnyTy
Definition: ASTContext.h:972
bool isFunctionType() const
Definition: Type.h:6646
LValueClassification
Definition: Expr.h:266
CanQualType getCanonicalType(QualType T) const
Return the canonical (structural) type corresponding to the specified potentially non-canonical type ...
Definition: ASTContext.h:2259
bool isLValueReferenceType() const
Definition: Type.h:6666
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:3050
bool isVoidType() const
Definition: Type.h:6933
bool isRValue() const
Definition: Expr.h:262
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:3683
An l-value expression is a reference to an object with independent storage.
Definition: Specifiers.h:131
This represents a decl that may have a name.
Definition: Decl.h:223
const LangOptions & getLangOpts() const
Definition: ASTContext.h:664
Expr * IgnoreParens() LLVM_READONLY
Skip past any parentheses which might surround this expression until reaching a fixed point...
Definition: Expr.cpp:2943