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"
22using namespace clang;
23
24typedef Expr::Classification Cl;
25
26static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E);
27static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D);
28static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T);
29static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E);
30static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E);
31static Cl::Kinds ClassifyConditional(ASTContext &Ctx,
32                                     const Expr *trueExpr,
33                                     const Expr *falseExpr);
34static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
35                                       Cl::Kinds Kind, SourceLocation &Loc);
36
37Cl 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())
51      kind = (kind == Cl::CL_LValue ? Cl::CL_AddressableVoid : Cl::CL_Void);
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:
60  case Cl::CL_AddressableVoid:
61  case Cl::CL_DuplicateVectorComponents:
62  case Cl::CL_MemberFunction:
63  case Cl::CL_SubObjCPropertySetting:
64  case Cl::CL_ClassTemporary:
65  case Cl::CL_ArrayTemporary:
66  case Cl::CL_ObjCMessageRValue:
67  case Cl::CL_PRValue: assert(getValueKind() == VK_RValue); break;
68  }
69
70  Cl::ModifiableType modifiable = Cl::CM_Untested;
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.
77static Cl::Kinds ClassifyTemporary(QualType T) {
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
88static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang,
89                                       const Expr *E,
90                                       ExprValueKind Kind) {
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
102static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
103  // This function takes the first stab at classifying expressions.
104  const LangOptions &Lang = Ctx.getLangOpts();
105
106  switch (E->getStmtClass()) {
107  case Stmt::NoStmtClass:
108#define ABSTRACT_STMT(Kind)
109#define STMT(Kind, Base) case Expr::Kind##Class:
110#define EXPR(Kind, Base)
111#include "clang/AST/StmtNodes.inc"
112    llvm_unreachable("cannot classify a statement");
113
114    // First come the expressions that are always lvalues, unconditionally.
115  case Expr::ObjCIsaExprClass:
116    // C++ [expr.prim.general]p1: A string literal is an lvalue.
117  case Expr::StringLiteralClass:
118    // @encode is equivalent to its string
119  case Expr::ObjCEncodeExprClass:
120    // __func__ and friends are too.
121  case Expr::PredefinedExprClass:
122    // Property references are lvalues
123  case Expr::ObjCSubscriptRefExprClass:
124  case Expr::ObjCPropertyRefExprClass:
125    // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...
126  case Expr::CXXTypeidExprClass:
127    // Unresolved lookups and uncorrected typos get classified as lvalues.
128    // FIXME: Is this wise? Should they get their own kind?
129  case Expr::UnresolvedLookupExprClass:
130  case Expr::UnresolvedMemberExprClass:
131  case Expr::TypoExprClass:
132  case Expr::CXXDependentScopeMemberExprClass:
133  case Expr::DependentScopeDeclRefExprClass:
134    // ObjC instance variables are lvalues
135    // FIXME: ObjC++0x might have different rules
136  case Expr::ObjCIvarRefExprClass:
137  case Expr::FunctionParmPackExprClass:
138  case Expr::MSPropertyRefExprClass:
139  case Expr::MSPropertySubscriptExprClass:
140  case Expr::OMPArraySectionExprClass:
141    return Cl::CL_LValue;
142
143    // C99 6.5.2.5p5 says that compound literals are lvalues.
144    // In C++, they're prvalue temporaries.
145  case Expr::CompoundLiteralExprClass:
146    return Ctx.getLangOpts().CPlusPlus ? ClassifyTemporary(E->getType())
147                                       : 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::CharacterLiteralClass:
164  case Expr::AddrLabelExprClass:
165  case Expr::CXXDeleteExprClass:
166  case Expr::ImplicitValueInitExprClass:
167  case Expr::BlockExprClass:
168  case Expr::FloatingLiteralClass:
169  case Expr::CXXNoexceptExprClass:
170  case Expr::CXXScalarValueInitExprClass:
171  case Expr::TypeTraitExprClass:
172  case Expr::ArrayTypeTraitExprClass:
173  case Expr::ExpressionTraitExprClass:
174  case Expr::ObjCSelectorExprClass:
175  case Expr::ObjCProtocolExprClass:
176  case Expr::ObjCStringLiteralClass:
177  case Expr::ObjCBoxedExprClass:
178  case Expr::ObjCArrayLiteralClass:
179  case Expr::ObjCDictionaryLiteralClass:
180  case Expr::ObjCBoolLiteralExprClass:
181  case Expr::ParenListExprClass:
182  case Expr::SizeOfPackExprClass:
183  case Expr::SubstNonTypeTemplateParmPackExprClass:
184  case Expr::AsTypeExprClass:
185  case Expr::ObjCIndirectCopyRestoreExprClass:
186  case Expr::AtomicExprClass:
187  case Expr::CXXFoldExprClass:
188  case Expr::NoInitExprClass:
189  case Expr::DesignatedInitUpdateExprClass:
190  case Expr::CoyieldExprClass:
191    return Cl::CL_PRValue;
192
193    // Next come the complicated cases.
194  case Expr::SubstNonTypeTemplateParmExprClass:
195    return ClassifyInternal(Ctx,
196                 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
197
198    // C++ [expr.sub]p1: The result is an lvalue of type "T".
199    // However, subscripting vector types is more like member access.
200  case Expr::ArraySubscriptExprClass:
201    if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
202      return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
203    return Cl::CL_LValue;
204
205    // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
206    //   function or variable and a prvalue otherwise.
207  case Expr::DeclRefExprClass:
208    if (E->getType() == Ctx.UnknownAnyTy)
209      return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
210               ? Cl::CL_PRValue : Cl::CL_LValue;
211    return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
212
213    // Member access is complex.
214  case Expr::MemberExprClass:
215    return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
216
217  case Expr::UnaryOperatorClass:
218    switch (cast<UnaryOperator>(E)->getOpcode()) {
219      // C++ [expr.unary.op]p1: The unary * operator performs indirection:
220      //   [...] the result is an lvalue referring to the object or function
221      //   to which the expression points.
222    case UO_Deref:
223      return Cl::CL_LValue;
224
225      // GNU extensions, simply look through them.
226    case UO_Extension:
227      return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
228
229    // Treat _Real and _Imag basically as if they were member
230    // expressions:  l-value only if the operand is a true l-value.
231    case UO_Real:
232    case UO_Imag: {
233      const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
234      Cl::Kinds K = ClassifyInternal(Ctx, Op);
235      if (K != Cl::CL_LValue) return K;
236
237      if (isa<ObjCPropertyRefExpr>(Op))
238        return Cl::CL_SubObjCPropertySetting;
239      return Cl::CL_LValue;
240    }
241
242      // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
243      //   lvalue, [...]
244      // Not so in C.
245    case UO_PreInc:
246    case UO_PreDec:
247      return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
248
249    default:
250      return Cl::CL_PRValue;
251    }
252
253  case Expr::OpaqueValueExprClass:
254    return ClassifyExprValueKind(Lang, E, E->getValueKind());
255
256    // Pseudo-object expressions can produce l-values with reference magic.
257  case Expr::PseudoObjectExprClass:
258    return ClassifyExprValueKind(Lang, E,
259                                 cast<PseudoObjectExpr>(E)->getValueKind());
260
261    // Implicit casts are lvalues if they're lvalue casts. Other than that, we
262    // only specifically record class temporaries.
263  case Expr::ImplicitCastExprClass:
264    return ClassifyExprValueKind(Lang, E, E->getValueKind());
265
266    // C++ [expr.prim.general]p4: The presence of parentheses does not affect
267    //   whether the expression is an lvalue.
268  case Expr::ParenExprClass:
269    return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
270
271    // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
272    // or a void expression if its result expression is, respectively, an
273    // lvalue, a function designator, or a void expression.
274  case Expr::GenericSelectionExprClass:
275    if (cast<GenericSelectionExpr>(E)->isResultDependent())
276      return Cl::CL_PRValue;
277    return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
278
279  case Expr::BinaryOperatorClass:
280  case Expr::CompoundAssignOperatorClass:
281    // C doesn't have any binary expressions that are lvalues.
282    if (Lang.CPlusPlus)
283      return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
284    return Cl::CL_PRValue;
285
286  case Expr::CallExprClass:
287  case Expr::CXXOperatorCallExprClass:
288  case Expr::CXXMemberCallExprClass:
289  case Expr::UserDefinedLiteralClass:
290  case Expr::CUDAKernelCallExprClass:
291    return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
292
293    // __builtin_choose_expr is equivalent to the chosen expression.
294  case Expr::ChooseExprClass:
295    return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
296
297    // Extended vector element access is an lvalue unless there are duplicates
298    // in the shuffle expression.
299  case Expr::ExtVectorElementExprClass:
300    if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
301      return Cl::CL_DuplicateVectorComponents;
302    if (cast<ExtVectorElementExpr>(E)->isArrow())
303      return Cl::CL_LValue;
304    return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
305
306    // Simply look at the actual default argument.
307  case Expr::CXXDefaultArgExprClass:
308    return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
309
310    // Same idea for default initializers.
311  case Expr::CXXDefaultInitExprClass:
312    return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
313
314    // Same idea for temporary binding.
315  case Expr::CXXBindTemporaryExprClass:
316    return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
317
318    // And the cleanups guard.
319  case Expr::ExprWithCleanupsClass:
320    return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
321
322    // Casts depend completely on the target type. All casts work the same.
323  case Expr::CStyleCastExprClass:
324  case Expr::CXXFunctionalCastExprClass:
325  case Expr::CXXStaticCastExprClass:
326  case Expr::CXXDynamicCastExprClass:
327  case Expr::CXXReinterpretCastExprClass:
328  case Expr::CXXConstCastExprClass:
329  case Expr::ObjCBridgedCastExprClass:
330    // Only in C++ can casts be interesting at all.
331    if (!Lang.CPlusPlus) return Cl::CL_PRValue;
332    return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
333
334  case Expr::CXXUnresolvedConstructExprClass:
335    return ClassifyUnnamed(Ctx,
336                      cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
337
338  case Expr::BinaryConditionalOperatorClass: {
339    if (!Lang.CPlusPlus) return Cl::CL_PRValue;
340    const BinaryConditionalOperator *co = cast<BinaryConditionalOperator>(E);
341    return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
342  }
343
344  case Expr::ConditionalOperatorClass: {
345    // Once again, only C++ is interesting.
346    if (!Lang.CPlusPlus) return Cl::CL_PRValue;
347    const ConditionalOperator *co = cast<ConditionalOperator>(E);
348    return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
349  }
350
351    // ObjC message sends are effectively function calls, if the target function
352    // is known.
353  case Expr::ObjCMessageExprClass:
354    if (const ObjCMethodDecl *Method =
355          cast<ObjCMessageExpr>(E)->getMethodDecl()) {
356      Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());
357      return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
358    }
359    return Cl::CL_PRValue;
360
361    // Some C++ expressions are always class temporaries.
362  case Expr::CXXConstructExprClass:
363  case Expr::CXXTemporaryObjectExprClass:
364  case Expr::LambdaExprClass:
365  case Expr::CXXStdInitializerListExprClass:
366    return Cl::CL_ClassTemporary;
367
368  case Expr::VAArgExprClass:
369    return ClassifyUnnamed(Ctx, E->getType());
370
371  case Expr::DesignatedInitExprClass:
372    return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
373
374  case Expr::StmtExprClass: {
375    const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
376    if (const Expr *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
377      return ClassifyUnnamed(Ctx, LastExpr->getType());
378    return Cl::CL_PRValue;
379  }
380
381  case Expr::CXXUuidofExprClass:
382    return Cl::CL_LValue;
383
384  case Expr::PackExpansionExprClass:
385    return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
386
387  case Expr::MaterializeTemporaryExprClass:
388    return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
389              ? Cl::CL_LValue
390              : Cl::CL_XValue;
391
392  case Expr::InitListExprClass:
393    // An init list can be an lvalue if it is bound to a reference and
394    // contains only one element. In that case, we look at that element
395    // for an exact classification. Init list creation takes care of the
396    // value kind for us, so we only need to fine-tune.
397    if (E->isRValue())
398      return ClassifyExprValueKind(Lang, E, E->getValueKind());
399    assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
400           "Only 1-element init lists can be glvalues.");
401    return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
402
403  case Expr::CoawaitExprClass:
404    return ClassifyInternal(Ctx, cast<CoawaitExpr>(E)->getResumeExpr());
405  }
406
407  llvm_unreachable("unhandled expression kind in classification");
408}
409
410/// ClassifyDecl - Return the classification of an expression referencing the
411/// given declaration.
412static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
413  // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
414  //   function, variable, or data member and a prvalue otherwise.
415  // In C, functions are not lvalues.
416  // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
417  // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
418  // special-case this.
419
420  if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
421    return Cl::CL_MemberFunction;
422
423  bool islvalue;
424  if (const NonTypeTemplateParmDecl *NTTParm =
425        dyn_cast<NonTypeTemplateParmDecl>(D))
426    islvalue = NTTParm->getType()->isReferenceType();
427  else
428    islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
429               isa<IndirectFieldDecl>(D) ||
430               (Ctx.getLangOpts().CPlusPlus &&
431                (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
432                 isa<FunctionTemplateDecl>(D)));
433
434  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
435}
436
437/// ClassifyUnnamed - Return the classification of an expression yielding an
438/// unnamed value of the given type. This applies in particular to function
439/// calls and casts.
440static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
441  // In C, function calls are always rvalues.
442  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
443
444  // C++ [expr.call]p10: A function call is an lvalue if the result type is an
445  //   lvalue reference type or an rvalue reference to function type, an xvalue
446  //   if the result type is an rvalue reference to object type, and a prvalue
447  //   otherwise.
448  if (T->isLValueReferenceType())
449    return Cl::CL_LValue;
450  const RValueReferenceType *RV = T->getAs<RValueReferenceType>();
451  if (!RV) // Could still be a class temporary, though.
452    return ClassifyTemporary(T);
453
454  return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
455}
456
457static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
458  if (E->getType() == Ctx.UnknownAnyTy)
459    return (isa<FunctionDecl>(E->getMemberDecl())
460              ? Cl::CL_PRValue : Cl::CL_LValue);
461
462  // Handle C first, it's easier.
463  if (!Ctx.getLangOpts().CPlusPlus) {
464    // C99 6.5.2.3p3
465    // For dot access, the expression is an lvalue if the first part is. For
466    // arrow access, it always is an lvalue.
467    if (E->isArrow())
468      return Cl::CL_LValue;
469    // ObjC property accesses are not lvalues, but get special treatment.
470    Expr *Base = E->getBase()->IgnoreParens();
471    if (isa<ObjCPropertyRefExpr>(Base))
472      return Cl::CL_SubObjCPropertySetting;
473    return ClassifyInternal(Ctx, Base);
474  }
475
476  NamedDecl *Member = E->getMemberDecl();
477  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
478  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
479  //   E1.E2 is an lvalue.
480  if (ValueDecl *Value = dyn_cast<ValueDecl>(Member))
481    if (Value->getType()->isReferenceType())
482      return Cl::CL_LValue;
483
484  //   Otherwise, one of the following rules applies.
485  //   -- If E2 is a static member [...] then E1.E2 is an lvalue.
486  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
487    return Cl::CL_LValue;
488
489  //   -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
490  //      E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
491  //      otherwise, it is a prvalue.
492  if (isa<FieldDecl>(Member)) {
493    // *E1 is an lvalue
494    if (E->isArrow())
495      return Cl::CL_LValue;
496    Expr *Base = E->getBase()->IgnoreParenImpCasts();
497    if (isa<ObjCPropertyRefExpr>(Base))
498      return Cl::CL_SubObjCPropertySetting;
499    return ClassifyInternal(Ctx, E->getBase());
500  }
501
502  //   -- If E2 is a [...] member function, [...]
503  //      -- If it refers to a static member function [...], then E1.E2 is an
504  //         lvalue; [...]
505  //      -- Otherwise [...] E1.E2 is a prvalue.
506  if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member))
507    return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
508
509  //   -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
510  // So is everything else we haven't handled yet.
511  return Cl::CL_PRValue;
512}
513
514static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {
515  assert(Ctx.getLangOpts().CPlusPlus &&
516         "This is only relevant for C++.");
517  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
518  // Except we override this for writes to ObjC properties.
519  if (E->isAssignmentOp())
520    return (E->getLHS()->getObjectKind() == OK_ObjCProperty
521              ? Cl::CL_PRValue : Cl::CL_LValue);
522
523  // C++ [expr.comma]p1: the result is of the same value category as its right
524  //   operand, [...].
525  if (E->getOpcode() == BO_Comma)
526    return ClassifyInternal(Ctx, E->getRHS());
527
528  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
529  //   is a pointer to a data member is of the same value category as its first
530  //   operand.
531  if (E->getOpcode() == BO_PtrMemD)
532    return (E->getType()->isFunctionType() ||
533            E->hasPlaceholderType(BuiltinType::BoundMember))
534             ? Cl::CL_MemberFunction
535             : ClassifyInternal(Ctx, E->getLHS());
536
537  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
538  //   second operand is a pointer to data member and a prvalue otherwise.
539  if (E->getOpcode() == BO_PtrMemI)
540    return (E->getType()->isFunctionType() ||
541            E->hasPlaceholderType(BuiltinType::BoundMember))
542             ? Cl::CL_MemberFunction
543             : Cl::CL_LValue;
544
545  // All other binary operations are prvalues.
546  return Cl::CL_PRValue;
547}
548
549static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
550                                     const Expr *False) {
551  assert(Ctx.getLangOpts().CPlusPlus &&
552         "This is only relevant for C++.");
553
554  // C++ [expr.cond]p2
555  //   If either the second or the third operand has type (cv) void,
556  //   one of the following shall hold:
557  if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
558    // The second or the third operand (but not both) is a (possibly
559    // parenthesized) throw-expression; the result is of the [...] value
560    // category of the other.
561    bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
562    bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
563    if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
564                                           : (FalseIsThrow ? True : nullptr))
565      return ClassifyInternal(Ctx, NonThrow);
566
567    //   [Otherwise] the result [...] is a prvalue.
568    return Cl::CL_PRValue;
569  }
570
571  // Note that at this point, we have already performed all conversions
572  // according to [expr.cond]p3.
573  // C++ [expr.cond]p4: If the second and third operands are glvalues of the
574  //   same value category [...], the result is of that [...] value category.
575  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
576  Cl::Kinds LCl = ClassifyInternal(Ctx, True),
577            RCl = ClassifyInternal(Ctx, False);
578  return LCl == RCl ? LCl : Cl::CL_PRValue;
579}
580
581static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
582                                       Cl::Kinds Kind, SourceLocation &Loc) {
583  // As a general rule, we only care about lvalues. But there are some rvalues
584  // for which we want to generate special results.
585  if (Kind == Cl::CL_PRValue) {
586    // For the sake of better diagnostics, we want to specifically recognize
587    // use of the GCC cast-as-lvalue extension.
588    if (const ExplicitCastExpr *CE =
589          dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
590      if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
591        Loc = CE->getExprLoc();
592        return Cl::CM_LValueCast;
593      }
594    }
595  }
596  if (Kind != Cl::CL_LValue)
597    return Cl::CM_RValue;
598
599  // This is the lvalue case.
600  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
601  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
602    return Cl::CM_Function;
603
604  // Assignment to a property in ObjC is an implicit setter access. But a
605  // setter might not exist.
606  if (const ObjCPropertyRefExpr *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
607    if (Expr->isImplicitProperty() &&
608        Expr->getImplicitPropertySetter() == nullptr)
609      return Cl::CM_NoSetterProperty;
610  }
611
612  CanQualType CT = Ctx.getCanonicalType(E->getType());
613  // Const stuff is obviously not modifiable.
614  if (CT.isConstQualified())
615    return Cl::CM_ConstQualified;
616  if (CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant)
617    return Cl::CM_ConstAddrSpace;
618
619  // Arrays are not modifiable, only their elements are.
620  if (CT->isArrayType())
621    return Cl::CM_ArrayType;
622  // Incomplete types are not modifiable.
623  if (CT->isIncompleteType())
624    return Cl::CM_IncompleteType;
625
626  // Records with any const fields (recursively) are not modifiable.
627  if (const RecordType *R = CT->getAs<RecordType>())
628    if (R->hasConstFields())
629      return Cl::CM_ConstQualified;
630
631  return Cl::CM_Modifiable;
632}
633
634Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
635  Classification VC = Classify(Ctx);
636  switch (VC.getKind()) {
637  case Cl::CL_LValue: return LV_Valid;
638  case Cl::CL_XValue: return LV_InvalidExpression;
639  case Cl::CL_Function: return LV_NotObjectType;
640  case Cl::CL_Void: return LV_InvalidExpression;
641  case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;
642  case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;
643  case Cl::CL_MemberFunction: return LV_MemberFunction;
644  case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
645  case Cl::CL_ClassTemporary: return LV_ClassTemporary;
646  case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
647  case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
648  case Cl::CL_PRValue: return LV_InvalidExpression;
649  }
650  llvm_unreachable("Unhandled kind");
651}
652
653Expr::isModifiableLvalueResult
654Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
655  SourceLocation dummy;
656  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
657  switch (VC.getKind()) {
658  case Cl::CL_LValue: break;
659  case Cl::CL_XValue: return MLV_InvalidExpression;
660  case Cl::CL_Function: return MLV_NotObjectType;
661  case Cl::CL_Void: return MLV_InvalidExpression;
662  case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;
663  case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;
664  case Cl::CL_MemberFunction: return MLV_MemberFunction;
665  case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
666  case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
667  case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
668  case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
669  case Cl::CL_PRValue:
670    return VC.getModifiable() == Cl::CM_LValueCast ?
671      MLV_LValueCast : MLV_InvalidExpression;
672  }
673  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
674  switch (VC.getModifiable()) {
675  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
676  case Cl::CM_Modifiable: return MLV_Valid;
677  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
678  case Cl::CM_Function: return MLV_NotObjectType;
679  case Cl::CM_LValueCast:
680    llvm_unreachable("CM_LValueCast and CL_LValue don't match");
681  case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
682  case Cl::CM_ConstQualified: return MLV_ConstQualified;
683  case Cl::CM_ConstAddrSpace: return MLV_ConstAddrSpace;
684  case Cl::CM_ArrayType: return MLV_ArrayType;
685  case Cl::CM_IncompleteType: return MLV_IncompleteType;
686  }
687  llvm_unreachable("Unhandled modifiable type");
688}
689