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//===--- 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 "llvm/Support/ErrorHandling.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/ExprObjC.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclTemplate.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 ConditionalOperator *E);
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.getLangOptions().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".
else if (TR->isVoidType() && !Ctx.getCanonicalType(TR).hasQualifiers())
kind = Cl::CL_Void;
}
Cl::ModifiableType modifiable = Cl::CM_Untested;
if (Loc)
modifiable = IsModifiable(Ctx, this, kind, *Loc);
return Classification(kind, modifiable);
}
static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
// This function takes the first stab at classifying expressions.
const LangOptions &Lang = Ctx.getLangOptions();
switch (E->getStmtClass()) {
// 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::ObjCPropertyRefExprClass:
case Expr::ObjCImplicitSetterGetterRefExprClass:
// 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:
// ObjC instance variables are lvalues
// FIXME: ObjC++0x might have different rules
case Expr::ObjCIvarRefExprClass:
// C99 6.5.2.5p5 says that compound literals are lvalues.
// FIXME: C++ might have a different opinion.
case Expr::CompoundLiteralExprClass:
return Cl::CL_LValue;
// Next come the complicated cases.
// C++ [expr.sub]p1: The result is an lvalue of type "T".
// However, 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());
return Cl::CL_LValue;
// 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:
return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
// We deal with names referenced from blocks the same way.
case Expr::BlockDeclRefExprClass:
return ClassifyDecl(Ctx, cast<BlockDeclRefExpr>(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 UnaryOperator::Deref:
return Cl::CL_LValue;
// GNU extensions, simply look through them.
case UnaryOperator::Real:
case UnaryOperator::Imag:
case UnaryOperator::Extension:
return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
// C++ [expr.pre.incr]p1: The result is the updated operand; it is an
// lvalue, [...]
// Not so in C.
case UnaryOperator::PreInc:
case UnaryOperator::PreDec:
return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
default:
return Cl::CL_PRValue;
}
// Implicit casts are lvalues if they're lvalue casts. Other than that, we
// only specifically record class temporaries.
case Expr::ImplicitCastExprClass:
if (cast<ImplicitCastExpr>(E)->isLvalueCast())
return Cl::CL_LValue;
return Lang.CPlusPlus && E->getType()->isRecordType() ?
Cl::CL_ClassTemporary : Cl::CL_PRValue;
// 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());
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:
return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType());
// __builtin_choose_expr is equivalent to the chosen expression.
case Expr::ChooseExprClass:
return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr(Ctx));
// Extended vector element access is an lvalue unless there are duplicates
// in the shuffle expression.
case Expr::ExtVectorElementExprClass:
return cast<ExtVectorElementExpr>(E)->containsDuplicateElements() ?
Cl::CL_DuplicateVectorComponents : Cl::CL_LValue;
// Simply look at the actual default argument.
case Expr::CXXDefaultArgExprClass:
return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
// Same idea for temporary binding.
case Expr::CXXBindTemporaryExprClass:
return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
// And the temporary lifetime guard.
case Expr::CXXExprWithTemporariesClass:
return ClassifyInternal(Ctx, cast<CXXExprWithTemporaries>(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:
// 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::ConditionalOperatorClass:
// Once again, only C++ is interesting.
if (!Lang.CPlusPlus) return Cl::CL_PRValue;
return ClassifyConditional(Ctx, cast<ConditionalOperator>(E));
// ObjC message sends are effectively function calls, if the target function
// is known.
case Expr::ObjCMessageExprClass:
if (const ObjCMethodDecl *Method =
cast<ObjCMessageExpr>(E)->getMethodDecl()) {
return ClassifyUnnamed(Ctx, Method->getResultType());
}
// Some C++ expressions are always class temporaries.
case Expr::CXXConstructExprClass:
case Expr::CXXTemporaryObjectExprClass:
case Expr::CXXZeroInitValueExprClass:
return Cl::CL_ClassTemporary;
// Everything we haven't handled is a prvalue.
default:
return Cl::CL_PRValue;
}
}
/// 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.
bool islvalue;
if (const NonTypeTemplateParmDecl *NTTParm =
dyn_cast<NonTypeTemplateParmDecl>(D))
islvalue = NTTParm->getType()->isReferenceType();
else
islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
(Ctx.getLangOptions().CPlusPlus &&
(isa<FunctionDecl>(D) || isa<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.getLangOptions().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 refernence to object type, and a prvalue
// otherwise.
if (T->isLValueReferenceType())
return Cl::CL_LValue;
const RValueReferenceType *RV = T->getAs<RValueReferenceType>();
if (!RV) // Could still be a class temporary, though.
return T->isRecordType() ? Cl::CL_ClassTemporary : Cl::CL_PRValue;
return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
}
static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
// Handle C first, it's easier.
if (!Ctx.getLangOptions().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();
if (isa<ObjCPropertyRefExpr>(Base) ||
isa<ObjCImplicitSetterGetterRefExpr>(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 (ValueDecl *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;
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 (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member))
return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
// -- 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.getLangOptions().CPlusPlus &&
"This is only relevant for C++.");
// C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
if (E->isAssignmentOp())
return Cl::CL_LValue;
// C++ [expr.comma]p1: the result is of the same value category as its right
// operand, [...].
if (E->getOpcode() == BinaryOperator::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() == BinaryOperator::PtrMemD)
return E->getType()->isFunctionType() ? 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() == BinaryOperator::PtrMemI)
return E->getType()->isFunctionType() ?
Cl::CL_MemberFunction : Cl::CL_LValue;
// All other binary operations are prvalues.
return Cl::CL_PRValue;
}
static Cl::Kinds ClassifyConditional(ASTContext &Ctx,
const ConditionalOperator *E) {
assert(Ctx.getLangOptions().CPlusPlus &&
"This is only relevant for C++.");
Expr *True = E->getTrueExpr();
Expr *False = E->getFalseExpr();
// C++ [expr.cond]p2
// If either the second or the third operand has type (cv) void, [...]
// the result [...] is a prvalue.
if (True->getType()->isVoidType() || False->getType()->isVoidType())
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 CStyleCastExpr *CE = dyn_cast<CStyleCastExpr>(E->IgnoreParens())){
if (CE->getSubExpr()->Classify(Ctx).isLValue()) {
Loc = CE->getLParenLoc();
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.getLangOptions().CPlusPlus && E->getType()->isFunctionType())
return Cl::CM_Function;
// You cannot assign to a variable outside a block from within the block if
// it is not marked __block, e.g.
// void takeclosure(void (^C)(void));
// void func() { int x = 1; takeclosure(^{ x = 7; }); }
if (const BlockDeclRefExpr *BDR = dyn_cast<BlockDeclRefExpr>(E)) {
if (!BDR->isByRef() && isa<VarDecl>(BDR->getDecl()))
return Cl::CM_NotBlockQualified;
}
// Assignment to a property in ObjC is an implicit setter access. But a
// setter might not exist.
if (const ObjCImplicitSetterGetterRefExpr *Expr =
dyn_cast<ObjCImplicitSetterGetterRefExpr>(E)) {
if (Expr->getSetterMethod() == 0)
return Cl::CM_NoSetterProperty;
}
CanQualType CT = Ctx.getCanonicalType(E->getType());
// Const stuff is obviously not modifiable.
if (CT.isConstQualified())
return Cl::CM_ConstQualified;
// 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>()) {
assert(!Ctx.getLangOptions().CPlusPlus &&
"C++ struct assignment should be resolved by the "
"copy assignment operator.");
if (R->hasConstFields())
return Cl::CM_ConstQualified;
}
return Cl::CM_Modifiable;
}
Expr::isLvalueResult Expr::isLvalue(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_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_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_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_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_NotBlockQualified: return MLV_NotBlockQualified;
case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
case Cl::CM_ConstQualified: return MLV_ConstQualified;
case Cl::CM_ArrayType: return MLV_ArrayType;
case Cl::CM_IncompleteType: return MLV_IncompleteType;
}
llvm_unreachable("Unhandled modifiable type");
}