Fix handling of const_cast from prvalue to rvalue reference: such a cast is
only permitted if the source object is of class type, and should materialize a
temporary for the reference to bind to.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184017 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaCast.cpp b/lib/Sema/SemaCast.cpp
index b4e7113..3b01c22 100644
--- a/lib/Sema/SemaCast.cpp
+++ b/lib/Sema/SemaCast.cpp
@@ -200,8 +200,9 @@
unsigned &msg, CastKind &Kind,
CXXCastPath &BasePath,
bool ListInitialization);
-static TryCastResult TryConstCast(Sema &Self, Expr *SrcExpr, QualType DestType,
- bool CStyle, unsigned &msg);
+static TryCastResult TryConstCast(Sema &Self, ExprResult &SrcExpr,
+ QualType DestType, bool CStyle,
+ unsigned &msg);
static TryCastResult TryReinterpretCast(Sema &Self, ExprResult &SrcExpr,
QualType DestType, bool CStyle,
const SourceRange &OpRange,
@@ -677,7 +678,7 @@
return;
unsigned msg = diag::err_bad_cxx_cast_generic;
- if (TryConstCast(Self, SrcExpr.get(), DestType, /*CStyle*/false, msg) != TC_Success
+ if (TryConstCast(Self, SrcExpr, DestType, /*CStyle*/false, msg) != TC_Success
&& msg != 0)
Self.Diag(OpRange.getBegin(), msg) << CT_Const
<< SrcExpr.get()->getType() << DestType << OpRange;
@@ -1447,12 +1448,26 @@
/// TryConstCast - See if a const_cast from source to destination is allowed,
/// and perform it if it is.
-static TryCastResult TryConstCast(Sema &Self, Expr *SrcExpr, QualType DestType,
- bool CStyle, unsigned &msg) {
+static TryCastResult TryConstCast(Sema &Self, ExprResult &SrcExpr,
+ QualType DestType, bool CStyle,
+ unsigned &msg) {
DestType = Self.Context.getCanonicalType(DestType);
- QualType SrcType = SrcExpr->getType();
+ QualType SrcType = SrcExpr.get()->getType();
+ bool NeedToMaterializeTemporary = false;
+
if (const ReferenceType *DestTypeTmp =DestType->getAs<ReferenceType>()) {
- if (isa<LValueReferenceType>(DestTypeTmp) && !SrcExpr->isLValue()) {
+ // C++11 5.2.11p4:
+ // if a pointer to T1 can be explicitly converted to the type "pointer to
+ // T2" using a const_cast, then the following conversions can also be
+ // made:
+ // -- an lvalue of type T1 can be explicitly converted to an lvalue of
+ // type T2 using the cast const_cast<T2&>;
+ // -- a glvalue of type T1 can be explicitly converted to an xvalue of
+ // type T2 using the cast const_cast<T2&&>; and
+ // -- if T1 is a class type, a prvalue of type T1 can be explicitly
+ // converted to an xvalue of type T2 using the cast const_cast<T2&&>.
+
+ if (isa<LValueReferenceType>(DestTypeTmp) && !SrcExpr.get()->isLValue()) {
// Cannot const_cast non-lvalue to lvalue reference type. But if this
// is C-style, static_cast might find a way, so we simply suggest a
// message and tell the parent to keep searching.
@@ -1460,18 +1475,29 @@
return TC_NotApplicable;
}
+ if (isa<RValueReferenceType>(DestTypeTmp) && SrcExpr.get()->isRValue()) {
+ if (!SrcType->isRecordType()) {
+ // Cannot const_cast non-class prvalue to rvalue reference type. But if
+ // this is C-style, static_cast can do this.
+ msg = diag::err_bad_cxx_cast_rvalue;
+ return TC_NotApplicable;
+ }
+
+ // Materialize the class prvalue so that the const_cast can bind a
+ // reference to it.
+ NeedToMaterializeTemporary = true;
+ }
+
// It's not completely clear under the standard whether we can
// const_cast bit-field gl-values. Doing so would not be
// intrinsically complicated, but for now, we say no for
// consistency with other compilers and await the word of the
// committee.
- if (SrcExpr->refersToBitField()) {
+ if (SrcExpr.get()->refersToBitField()) {
msg = diag::err_bad_cxx_cast_bitfield;
return TC_NotApplicable;
}
- // C++ 5.2.11p4: An lvalue of type T1 can be [cast] to an lvalue of type T2
- // [...] if a pointer to T1 can be [cast] to the type pointer to T2.
DestType = Self.Context.getPointerType(DestTypeTmp->getPointeeType());
SrcType = Self.Context.getPointerType(SrcType);
}
@@ -1525,6 +1551,13 @@
if (SrcType != DestType)
return TC_NotApplicable;
+ if (NeedToMaterializeTemporary)
+ // This is a const_cast from a class prvalue to an rvalue reference type.
+ // Materialize a temporary to store the result of the conversion.
+ SrcExpr = new (Self.Context) MaterializeTemporaryExpr(
+ SrcType, SrcExpr.take(), /*IsLValueReference*/ false,
+ /*ExtendingDecl*/ 0);
+
return TC_Success;
}
@@ -1992,8 +2025,10 @@
// even if a cast resulting from that interpretation is ill-formed.
// In plain language, this means trying a const_cast ...
unsigned msg = diag::err_bad_cxx_cast_generic;
- TryCastResult tcr = TryConstCast(Self, SrcExpr.get(), DestType,
+ TryCastResult tcr = TryConstCast(Self, SrcExpr, DestType,
/*CStyle*/true, msg);
+ if (SrcExpr.isInvalid())
+ return;
if (tcr == TC_Success)
Kind = CK_NoOp;