//===- ExprClassification.cpp - Expression AST Node Implementation --------===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This file implements Expr::classify.

//

//===----------------------------------------------------------------------===//

#include "clang/AST/Expr.h"

#include "clang/AST/ASTContext.h"

#include "clang/AST/DeclCXX.h"

#include "clang/AST/DeclObjC.h"

#include "clang/AST/DeclTemplate.h"

#include "clang/AST/ExprCXX.h"

#include "clang/AST/ExprObjC.h"

#include "llvm/Support/ErrorHandling.h"

using namespace clang;

using Cl = Expr::Classification;

static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E);

static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D);

static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T);

static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E);

static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E);

static Cl::Kinds ClassifyConditional(ASTContext &Ctx,

                                     const Expr *trueExpr,

                                     const Expr *falseExpr);

static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,

                                       Cl::Kinds Kind, SourceLocation &Loc);

Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {

  assert(!TR->isReferenceType() && "Expressions can't have reference type.");

  Cl::Kinds kind = ClassifyInternal(Ctx, this);

  // C99 6.3.2.1: An lvalue is an expression with an object type or an

  //   incomplete type other than void.

  if (!Ctx.getLangOpts().CPlusPlus) {

    // Thus, no functions.

    if (TR->isFunctionType() || TR == Ctx.OverloadTy)

      kind = Cl::CL_Function;

    // No void either, but qualified void is OK because it is "other than void".

    // Void "lvalues" are classified as addressable void values, which are void

    // expressions whose address can be taken.

    else if (TR->isVoidType() && !TR.hasQualifiers())

      kind = (kind == Cl::CL_LValue ? Cl::CL_AddressableVoid : Cl::CL_Void);

  }

  // Enable this assertion for testing.

  switch (kind) {

  case Cl::CL_LValue:

    assert(isLValue());

    break;

  case Cl::CL_XValue:

    assert(isXValue());

    break;

  case Cl::CL_Function:

  case Cl::CL_Void:

  case Cl::CL_AddressableVoid:

  case Cl::CL_DuplicateVectorComponents:

  case Cl::CL_MemberFunction:

  case Cl::CL_SubObjCPropertySetting:

  case Cl::CL_ClassTemporary:

  case Cl::CL_ArrayTemporary:

  case Cl::CL_ObjCMessageRValue:

  case Cl::CL_PRValue:

    assert(isPRValue());

    break;

  }

  Cl::ModifiableType modifiable = Cl::CM_Untested;

  if (Loc)

    modifiable = IsModifiable(Ctx, this, kind, *Loc);

  return Classification(kind, modifiable);

}

/// Classify an expression which creates a temporary, based on its type.

static Cl::Kinds ClassifyTemporary(QualType T) {

  if (T->isRecordType())

    return Cl::CL_ClassTemporary;

  if (T->isArrayType())

    return Cl::CL_ArrayTemporary;

  // No special classification: these don't behave differently from normal

  // prvalues.

  return Cl::CL_PRValue;

}

static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang,

                                       const Expr *E,

                                       ExprValueKind Kind) {

  switch (Kind) {

  case VK_PRValue:

    return Lang.CPlusPlus ? ClassifyTemporary(E->getType()) : Cl::CL_PRValue;

  case VK_LValue:

    return Cl::CL_LValue;

  case VK_XValue:

    return Cl::CL_XValue;

  }

  llvm_unreachable("Invalid value category of implicit cast.");

}

static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {

  // This function takes the first stab at classifying expressions.

  const LangOptions &Lang = Ctx.getLangOpts();

  switch (E->getStmtClass()) {

  case Stmt::NoStmtClass:

#define ABSTRACT_STMT(Kind)

#define STMT(Kind, Base) case Expr::Kind##Class:

#define EXPR(Kind, Base)

#include "clang/AST/StmtNodes.inc"

    llvm_unreachable("cannot classify a statement");

    // First come the expressions that are always lvalues, unconditionally.

  case Expr::ObjCIsaExprClass:

    // C++ [expr.prim.general]p1: A string literal is an lvalue.

  case Expr::StringLiteralClass:

    // @encode is equivalent to its string

  case Expr::ObjCEncodeExprClass:

    // __func__ and friends are too.

  case Expr::PredefinedExprClass:

    // Property references are lvalues

  case Expr::ObjCSubscriptRefExprClass:

  case Expr::ObjCPropertyRefExprClass:

    // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...

  case Expr::CXXTypeidExprClass:

  case Expr::CXXUuidofExprClass:

    // Unresolved lookups and uncorrected typos get classified as lvalues.

    // FIXME: Is this wise? Should they get their own kind?

  case Expr::UnresolvedLookupExprClass:

  case Expr::UnresolvedMemberExprClass:

  case Expr::TypoExprClass:

  case Expr::DependentCoawaitExprClass:

  case Expr::CXXDependentScopeMemberExprClass:

  case Expr::DependentScopeDeclRefExprClass:

    // ObjC instance variables are lvalues

    // FIXME: ObjC++0x might have different rules

  case Expr::ObjCIvarRefExprClass:

  case Expr::FunctionParmPackExprClass:

  case Expr::MSPropertyRefExprClass:

  case Expr::MSPropertySubscriptExprClass:

  case Expr::OMPArraySectionExprClass:

  case Expr::OMPArrayShapingExprClass:

  case Expr::OMPIteratorExprClass:

    return Cl::CL_LValue;

    // C99 6.5.2.5p5 says that compound literals are lvalues.

    // In C++, they're prvalue temporaries, except for file-scope arrays.

  case Expr::CompoundLiteralExprClass:

    return !E->isLValue() ? ClassifyTemporary(E->getType()) : Cl::CL_LValue;

    // Expressions that are prvalues.

  case Expr::CXXBoolLiteralExprClass:

  case Expr::CXXPseudoDestructorExprClass:

  case Expr::UnaryExprOrTypeTraitExprClass:

  case Expr::CXXNewExprClass:

  case Expr::CXXNullPtrLiteralExprClass:

  case Expr::ImaginaryLiteralClass:

  case Expr::GNUNullExprClass:

  case Expr::OffsetOfExprClass:

  case Expr::CXXThrowExprClass:

  case Expr::ShuffleVectorExprClass:

  case Expr::ConvertVectorExprClass:

  case Expr::IntegerLiteralClass:

  case Expr::FixedPointLiteralClass:

  case Expr::CharacterLiteralClass:

  case Expr::AddrLabelExprClass:

  case Expr::CXXDeleteExprClass:

  case Expr::ImplicitValueInitExprClass:

  case Expr::BlockExprClass:

  case Expr::FloatingLiteralClass:

  case Expr::CXXNoexceptExprClass:

  case Expr::CXXScalarValueInitExprClass:

  case Expr::TypeTraitExprClass:

  case Expr::ArrayTypeTraitExprClass:

  case Expr::ExpressionTraitExprClass:

  case Expr::ObjCSelectorExprClass:

  case Expr::ObjCProtocolExprClass:

  case Expr::ObjCStringLiteralClass:

  case Expr::ObjCBoxedExprClass:

  case Expr::ObjCArrayLiteralClass:

  case Expr::ObjCDictionaryLiteralClass:

  case Expr::ObjCBoolLiteralExprClass:

  case Expr::ObjCAvailabilityCheckExprClass:

  case Expr::ParenListExprClass:

  case Expr::SizeOfPackExprClass:

  case Expr::SubstNonTypeTemplateParmPackExprClass:

  case Expr::AsTypeExprClass:

  case Expr::ObjCIndirectCopyRestoreExprClass:

  case Expr::AtomicExprClass:

  case Expr::CXXFoldExprClass:

  case Expr::ArrayInitLoopExprClass:

  case Expr::ArrayInitIndexExprClass:

  case Expr::NoInitExprClass:

  case Expr::DesignatedInitUpdateExprClass:

  case Expr::SourceLocExprClass:

  case Expr::ConceptSpecializationExprClass:

  case Expr::RequiresExprClass:

    return Cl::CL_PRValue;

  // Make HLSL this reference-like

  case Expr::CXXThisExprClass:

    return Lang.HLSL ? Cl::CL_LValue : Cl::CL_PRValue;

  case Expr::ConstantExprClass:

    return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr());

    // Next come the complicated cases.

  case Expr::SubstNonTypeTemplateParmExprClass:

    return ClassifyInternal(Ctx,

                 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());

    // C, C++98 [expr.sub]p1: The result is an lvalue of type "T".

    // C++11 (DR1213): in the case of an array operand, the result is an lvalue

    //                 if that operand is an lvalue and an xvalue otherwise.

    // Subscripting vector types is more like member access.

  case Expr::ArraySubscriptExprClass:

    if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())

      return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());

    if (Lang.CPlusPlus11) {

      // Step over the array-to-pointer decay if present, but not over the

      // temporary materialization.

      auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts();

      if (Base->getType()->isArrayType())

        return ClassifyInternal(Ctx, Base);

    }

    return Cl::CL_LValue;

  // Subscripting matrix types behaves like member accesses.

  case Expr::MatrixSubscriptExprClass:

    return ClassifyInternal(Ctx, cast<MatrixSubscriptExpr>(E)->getBase());

    // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a

    //   function or variable and a prvalue otherwise.

  case Expr::DeclRefExprClass:

    if (E->getType() == Ctx.UnknownAnyTy)

      return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())

               ? Cl::CL_PRValue : Cl::CL_LValue;

    return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());

    // Member access is complex.

  case Expr::MemberExprClass:

    return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));

  case Expr::UnaryOperatorClass:

    switch (cast<UnaryOperator>(E)->getOpcode()) {

      // C++ [expr.unary.op]p1: The unary * operator performs indirection:

      //   [...] the result is an lvalue referring to the object or function

      //   to which the expression points.

    case UO_Deref:

      return Cl::CL_LValue;

      // GNU extensions, simply look through them.

    case UO_Extension:

      return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());

    // Treat _Real and _Imag basically as if they were member

    // expressions:  l-value only if the operand is a true l-value.

    case UO_Real:

    case UO_Imag: {

      const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();

      Cl::Kinds K = ClassifyInternal(Ctx, Op);

      if (K != Cl::CL_LValue) return K;

      if (isa<ObjCPropertyRefExpr>(Op))

        return Cl::CL_SubObjCPropertySetting;

      return Cl::CL_LValue;

    }

      // C++ [expr.pre.incr]p1: The result is the updated operand; it is an

      //   lvalue, [...]

      // Not so in C.

    case UO_PreInc:

    case UO_PreDec:

      return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;

    default:

      return Cl::CL_PRValue;

    }

  case Expr::RecoveryExprClass:

  case Expr::OpaqueValueExprClass:

    return ClassifyExprValueKind(Lang, E, E->getValueKind());

    // Pseudo-object expressions can produce l-values with reference magic.

  case Expr::PseudoObjectExprClass:

    return ClassifyExprValueKind(Lang, E,

                                 cast<PseudoObjectExpr>(E)->getValueKind());

    // Implicit casts are lvalues if they're lvalue casts. Other than that, we

    // only specifically record class temporaries.

  case Expr::ImplicitCastExprClass:

    return ClassifyExprValueKind(Lang, E, E->getValueKind());

    // C++ [expr.prim.general]p4: The presence of parentheses does not affect

    //   whether the expression is an lvalue.

  case Expr::ParenExprClass:

    return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());

    // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,

    // or a void expression if its result expression is, respectively, an

    // lvalue, a function designator, or a void expression.

  case Expr::GenericSelectionExprClass:

    if (cast<GenericSelectionExpr>(E)->isResultDependent())

      return Cl::CL_PRValue;

    return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());

  case Expr::BinaryOperatorClass:

  case Expr::CompoundAssignOperatorClass:

    // C doesn't have any binary expressions that are lvalues.

    if (Lang.CPlusPlus)

      return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));

    return Cl::CL_PRValue;

  case Expr::CallExprClass:

  case Expr::CXXOperatorCallExprClass:

  case Expr::CXXMemberCallExprClass:

  case Expr::UserDefinedLiteralClass:

  case Expr::CUDAKernelCallExprClass:

    return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));

  case Expr::CXXRewrittenBinaryOperatorClass:

    return ClassifyInternal(

        Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm());

    // __builtin_choose_expr is equivalent to the chosen expression.

  case Expr::ChooseExprClass:

    return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());

    // Extended vector element access is an lvalue unless there are duplicates

    // in the shuffle expression.

  case Expr::ExtVectorElementExprClass:

    if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())

      return Cl::CL_DuplicateVectorComponents;

    if (cast<ExtVectorElementExpr>(E)->isArrow())

      return Cl::CL_LValue;

    return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());

    // Simply look at the actual default argument.

  case Expr::CXXDefaultArgExprClass:

    return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());

    // Same idea for default initializers.

  case Expr::CXXDefaultInitExprClass:

    return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());

    // Same idea for temporary binding.

  case Expr::CXXBindTemporaryExprClass:

    return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());

    // And the cleanups guard.

  case Expr::ExprWithCleanupsClass:

    return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());

    // Casts depend completely on the target type. All casts work the same.

  case Expr::CStyleCastExprClass:

  case Expr::CXXFunctionalCastExprClass:

  case Expr::CXXStaticCastExprClass:

  case Expr::CXXDynamicCastExprClass:

  case Expr::CXXReinterpretCastExprClass:

  case Expr::CXXConstCastExprClass:

  case Expr::CXXAddrspaceCastExprClass:

  case Expr::ObjCBridgedCastExprClass:

  case Expr::BuiltinBitCastExprClass:

    // Only in C++ can casts be interesting at all.

    if (!Lang.CPlusPlus) return Cl::CL_PRValue;

    return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());

  case Expr::CXXUnresolvedConstructExprClass:

    return ClassifyUnnamed(Ctx,

                      cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());

  case Expr::BinaryConditionalOperatorClass: {

    if (!Lang.CPlusPlus) return Cl::CL_PRValue;

    const auto *co = cast<BinaryConditionalOperator>(E);

    return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());

  }

  case Expr::ConditionalOperatorClass: {

    // Once again, only C++ is interesting.

    if (!Lang.CPlusPlus) return Cl::CL_PRValue;

    const auto *co = cast<ConditionalOperator>(E);

    return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());

  }

    // ObjC message sends are effectively function calls, if the target function

    // is known.

  case Expr::ObjCMessageExprClass:

    if (const ObjCMethodDecl *Method =

          cast<ObjCMessageExpr>(E)->getMethodDecl()) {

      Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());

      return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;

    }

    return Cl::CL_PRValue;

    // Some C++ expressions are always class temporaries.

  case Expr::CXXConstructExprClass:

  case Expr::CXXInheritedCtorInitExprClass:

  case Expr::CXXTemporaryObjectExprClass:

  case Expr::LambdaExprClass:

  case Expr::CXXStdInitializerListExprClass:

    return Cl::CL_ClassTemporary;

  case Expr::VAArgExprClass:

    return ClassifyUnnamed(Ctx, E->getType());

  case Expr::DesignatedInitExprClass:

    return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());

  case Expr::StmtExprClass: {

    const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();

    if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))

      return ClassifyUnnamed(Ctx, LastExpr->getType());

    return Cl::CL_PRValue;

  }

  case Expr::PackExpansionExprClass:

    return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());

  case Expr::MaterializeTemporaryExprClass:

    return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()

              ? Cl::CL_LValue

              : Cl::CL_XValue;

  case Expr::InitListExprClass:

    // An init list can be an lvalue if it is bound to a reference and

    // contains only one element. In that case, we look at that element

    // for an exact classification. Init list creation takes care of the

    // value kind for us, so we only need to fine-tune.

    if (E->isPRValue())

      return ClassifyExprValueKind(Lang, E, E->getValueKind());

    assert(cast<InitListExpr>(E)->getNumInits() == 1 &&

           "Only 1-element init lists can be glvalues.");

    return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));

  case Expr::CoawaitExprClass:

  case Expr::CoyieldExprClass:

    return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr());

  case Expr::SYCLUniqueStableNameExprClass:

    return Cl::CL_PRValue;

    break;

  case Expr::CXXParenListInitExprClass:

    if (isa<ArrayType>(E->getType()))

      return Cl::CL_ArrayTemporary;

    return Cl::CL_ClassTemporary;

  }

  llvm_unreachable("unhandled expression kind in classification");

}

/// ClassifyDecl - Return the classification of an expression referencing the

/// given declaration.

static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {

  // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a

  //   function, variable, or data member and a prvalue otherwise.

  // In C, functions are not lvalues.

  // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an

  // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to

  // special-case this.

  if (const auto *M = dyn_cast<CXXMethodDecl>(D)) {

    if (M->isImplicitObjectMemberFunction())

      return Cl::CL_MemberFunction;

    if (M->isStatic())

      return Cl::CL_LValue;

    return Cl::CL_PRValue;

  }

  bool islvalue;

  if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))

    islvalue = NTTParm->getType()->isReferenceType() ||

               NTTParm->getType()->isRecordType();

  else

    islvalue =

        isa<VarDecl, FieldDecl, IndirectFieldDecl, BindingDecl, MSGuidDecl,

            UnnamedGlobalConstantDecl, TemplateParamObjectDecl>(D) ||

        (Ctx.getLangOpts().CPlusPlus &&

         (isa<FunctionDecl, MSPropertyDecl, FunctionTemplateDecl>(D)));

  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;

}

/// ClassifyUnnamed - Return the classification of an expression yielding an

/// unnamed value of the given type. This applies in particular to function

/// calls and casts.

static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {

  // In C, function calls are always rvalues.

  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;

  // C++ [expr.call]p10: A function call is an lvalue if the result type is an

  //   lvalue reference type or an rvalue reference to function type, an xvalue

  //   if the result type is an rvalue reference to object type, and a prvalue

  //   otherwise.

  if (T->isLValueReferenceType())

    return Cl::CL_LValue;

  const auto *RV = T->getAs<RValueReferenceType>();

  if (!RV) // Could still be a class temporary, though.

    return ClassifyTemporary(T);

  return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;

}

static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {

  if (E->getType() == Ctx.UnknownAnyTy)

    return (isa<FunctionDecl>(E->getMemberDecl())

              ? Cl::CL_PRValue : Cl::CL_LValue);

  // Handle C first, it's easier.

  if (!Ctx.getLangOpts().CPlusPlus) {

    // C99 6.5.2.3p3

    // For dot access, the expression is an lvalue if the first part is. For

    // arrow access, it always is an lvalue.

    if (E->isArrow())

      return Cl::CL_LValue;

    // ObjC property accesses are not lvalues, but get special treatment.

    Expr *Base = E->getBase()->IgnoreParens();

    if (isa<ObjCPropertyRefExpr>(Base))

      return Cl::CL_SubObjCPropertySetting;

    return ClassifyInternal(Ctx, Base);

  }

  NamedDecl *Member = E->getMemberDecl();

  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.

  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then

  //   E1.E2 is an lvalue.

  if (const auto *Value = dyn_cast<ValueDecl>(Member))

    if (Value->getType()->isReferenceType())

      return Cl::CL_LValue;

  //   Otherwise, one of the following rules applies.

  //   -- If E2 is a static member [...] then E1.E2 is an lvalue.

  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())

    return Cl::CL_LValue;

  //   -- If E2 is a non-static data member [...]. If E1 is an lvalue, then

  //      E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;

  //      otherwise, it is a prvalue.

  if (isa<FieldDecl>(Member)) {

    // *E1 is an lvalue

    if (E->isArrow())

      return Cl::CL_LValue;

    Expr *Base = E->getBase()->IgnoreParenImpCasts();

    if (isa<ObjCPropertyRefExpr>(Base))

      return Cl::CL_SubObjCPropertySetting;

    return ClassifyInternal(Ctx, E->getBase());

  }

  //   -- If E2 is a [...] member function, [...]

  //      -- If it refers to a static member function [...], then E1.E2 is an

  //         lvalue; [...]

  //      -- Otherwise [...] E1.E2 is a prvalue.

  if (const auto *Method = dyn_cast<CXXMethodDecl>(Member)) {

    if (Method->isStatic())

      return Cl::CL_LValue;

    if (Method->isImplicitObjectMemberFunction())

      return Cl::CL_MemberFunction;

    return Cl::CL_PRValue;

  }

  //   -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.

  // So is everything else we haven't handled yet.

  return Cl::CL_PRValue;

}

static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {

  assert(Ctx.getLangOpts().CPlusPlus &&

         "This is only relevant for C++.");

  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.

  // Except we override this for writes to ObjC properties.

  if (E->isAssignmentOp())

    return (E->getLHS()->getObjectKind() == OK_ObjCProperty

              ? Cl::CL_PRValue : Cl::CL_LValue);

  // C++ [expr.comma]p1: the result is of the same value category as its right

  //   operand, [...].

  if (E->getOpcode() == BO_Comma)

    return ClassifyInternal(Ctx, E->getRHS());

  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand

  //   is a pointer to a data member is of the same value category as its first

  //   operand.

  if (E->getOpcode() == BO_PtrMemD)

    return (E->getType()->isFunctionType() ||

            E->hasPlaceholderType(BuiltinType::BoundMember))

             ? Cl::CL_MemberFunction

             : ClassifyInternal(Ctx, E->getLHS());

  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its

  //   second operand is a pointer to data member and a prvalue otherwise.

  if (E->getOpcode() == BO_PtrMemI)

    return (E->getType()->isFunctionType() ||

            E->hasPlaceholderType(BuiltinType::BoundMember))

             ? Cl::CL_MemberFunction

             : Cl::CL_LValue;

  // All other binary operations are prvalues.

  return Cl::CL_PRValue;

}

static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,

                                     const Expr *False) {

  assert(Ctx.getLangOpts().CPlusPlus &&

         "This is only relevant for C++.");

  // C++ [expr.cond]p2

  //   If either the second or the third operand has type (cv) void,

  //   one of the following shall hold:

  if (True->getType()->isVoidType() || False->getType()->isVoidType()) {

    // The second or the third operand (but not both) is a (possibly

    // parenthesized) throw-expression; the result is of the [...] value

    // category of the other.

    bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());

    bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());

    if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)

                                           : (FalseIsThrow ? True : nullptr))

      return ClassifyInternal(Ctx, NonThrow);

    //   [Otherwise] the result [...] is a prvalue.

    return Cl::CL_PRValue;

  }

  // Note that at this point, we have already performed all conversions

  // according to [expr.cond]p3.

  // C++ [expr.cond]p4: If the second and third operands are glvalues of the

  //   same value category [...], the result is of that [...] value category.

  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.

  Cl::Kinds LCl = ClassifyInternal(Ctx, True),

            RCl = ClassifyInternal(Ctx, False);

  return LCl == RCl ? LCl : Cl::CL_PRValue;

}

static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,

                                       Cl::Kinds Kind, SourceLocation &Loc) {

  // As a general rule, we only care about lvalues. But there are some rvalues

  // for which we want to generate special results.

  if (Kind == Cl::CL_PRValue) {

    // For the sake of better diagnostics, we want to specifically recognize

    // use of the GCC cast-as-lvalue extension.

    if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {

      if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {

        Loc = CE->getExprLoc();

        return Cl::CM_LValueCast;

      }

    }

  }

  if (Kind != Cl::CL_LValue)

    return Cl::CM_RValue;

  // This is the lvalue case.

  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)

  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())

    return Cl::CM_Function;

  // Assignment to a property in ObjC is an implicit setter access. But a

  // setter might not exist.

  if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {

    if (Expr->isImplicitProperty() &&

        Expr->getImplicitPropertySetter() == nullptr)

      return Cl::CM_NoSetterProperty;

  }

  CanQualType CT = Ctx.getCanonicalType(E->getType());

  // Const stuff is obviously not modifiable.

  if (CT.isConstQualified())

    return Cl::CM_ConstQualified;

  if (Ctx.getLangOpts().OpenCL &&

      CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant)

    return Cl::CM_ConstAddrSpace;

  // Arrays are not modifiable, only their elements are.

  if (CT->isArrayType())

    return Cl::CM_ArrayType;

  // Incomplete types are not modifiable.

  if (CT->isIncompleteType())

    return Cl::CM_IncompleteType;

  // Records with any const fields (recursively) are not modifiable.

  if (const RecordType *R = CT->getAs<RecordType>())

    if (R->hasConstFields())

      return Cl::CM_ConstQualifiedField;

  return Cl::CM_Modifiable;

}

Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {

  Classification VC = Classify(Ctx);

  switch (VC.getKind()) {

  case Cl::CL_LValue: return LV_Valid;

  case Cl::CL_XValue: return LV_InvalidExpression;

  case Cl::CL_Function: return LV_NotObjectType;

  case Cl::CL_Void: return LV_InvalidExpression;

  case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;

  case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;

  case Cl::CL_MemberFunction: return LV_MemberFunction;

  case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;

  case Cl::CL_ClassTemporary: return LV_ClassTemporary;

  case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;

  case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;

  case Cl::CL_PRValue: return LV_InvalidExpression;

  }

  llvm_unreachable("Unhandled kind");

}

Expr::isModifiableLvalueResult

Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {

  SourceLocation dummy;

  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);

  switch (VC.getKind()) {

  case Cl::CL_LValue: break;

  case Cl::CL_XValue: return MLV_InvalidExpression;

  case Cl::CL_Function: return MLV_NotObjectType;

  case Cl::CL_Void: return MLV_InvalidExpression;

  case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;

  case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;

  case Cl::CL_MemberFunction: return MLV_MemberFunction;

  case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;

  case Cl::CL_ClassTemporary: return MLV_ClassTemporary;

  case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;

  case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;

  case Cl::CL_PRValue:

    return VC.getModifiable() == Cl::CM_LValueCast ?

      MLV_LValueCast : MLV_InvalidExpression;

  }

  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");

  switch (VC.getModifiable()) {

  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");

  case Cl::CM_Modifiable: return MLV_Valid;

  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");

  case Cl::CM_Function: return MLV_NotObjectType;

  case Cl::CM_LValueCast:

    llvm_unreachable("CM_LValueCast and CL_LValue don't match");

  case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;

  case Cl::CM_ConstQualified: return MLV_ConstQualified;

  case Cl::CM_ConstQualifiedField: return MLV_ConstQualifiedField;

  case Cl::CM_ConstAddrSpace: return MLV_ConstAddrSpace;

  case Cl::CM_ArrayType: return MLV_ArrayType;

  case Cl::CM_IncompleteType: return MLV_IncompleteType;

  }

  llvm_unreachable("Unhandled modifiable type");

}