path: root/lib/AST/ExprClassification.cpp

//===--- ExprClassification.cpp - Expression AST Node Implementation ------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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;

typedef Expr::Classification Cl;

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(getValueKind() == VK_LValue); break;
  case Cl::CL_XValue: assert(getValueKind() == VK_XValue); 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(getValueKind() == VK_RValue); 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_RValue:
    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:
    // Unresolved lookups get classified as lvalues.
    // FIXME: Is this wise? Should they get their own kind?
  case Expr::UnresolvedLookupExprClass:
  case Expr::UnresolvedMemberExprClass:
  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:
    return Cl::CL_LValue;

    // C99 6.5.2.5p5 says that compound literals are lvalues.
    // In C++, they're prvalue temporaries.
  case Expr::CompoundLiteralExprClass:
    return Ctx.getLangOpts().CPlusPlus ? ClassifyTemporary(E->getType())
                                       : Cl::CL_LValue;

    // Expressions that are prvalues.
  case Expr::CXXBoolLiteralExprClass:
  case Expr::CXXPseudoDestructorExprClass:
  case Expr::UnaryExprOrTypeTraitExprClass:
  case Expr::CXXNewExprClass:
  case Expr::CXXThisExprClass:
  case Expr::CXXNullPtrLiteralExprClass:
  case Expr::ImaginaryLiteralClass:
  case Expr::GNUNullExprClass:
  case Expr::OffsetOfExprClass:
  case Expr::CXXThrowExprClass:
  case Expr::ShuffleVectorExprClass:
  case Expr::IntegerLiteralClass:
  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::UnaryTypeTraitExprClass:
  case Expr::BinaryTypeTraitExprClass:
  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::ParenListExprClass:
  case Expr::SizeOfPackExprClass:
  case Expr::SubstNonTypeTemplateParmPackExprClass:
  case Expr::AsTypeExprClass:
  case Expr::ObjCIndirectCopyRestoreExprClass:
  case Expr::AtomicExprClass:
    return Cl::CL_PRValue;