[cfe-commits] r138715 - in /cfe/trunk: lib/Sema/SemaExpr.cpp test/CXX/special/class.temporary/p1.cpp

[Johannes Schaub]

John McCall wrote:

Hi, I have a comment below.

> Modified: cfe/trunk/lib/Sema/SemaExpr.cpp
> URL:
> http://llvm.org/viewvc/llvm-
project/cfe/trunk/lib/Sema/SemaExpr.cpp?rev=138715&r1=138714&r2=138715&view=diff
> 
==============================================================================
> --- cfe/trunk/lib/Sema/SemaExpr.cpp (original) +++
> cfe/trunk/lib/Sema/SemaExpr.cpp Sat Aug 27 17:06:17 2011 @@ -443,9 +443,15
> @@
>    if (Ty->isSpecificBuiltinType(BuiltinType::Float))
>      E = ImpCastExprToType(E, Context.DoubleTy, CK_FloatingCast).take();
>  
> -  // C++ includes lvalue-to-rvalue conversion as a default argument
> -  // promotion.  If we have a gl-value, initialize a temporary.
> -  if (getLangOptions().CPlusPlus && E->isGLValue()) {
> +  // C++ performs lvalue-to-rvalue conversion as a default argument
> +  // promotion.  If we still have a gl-value after usual unary
> +  // conversion, we must have an l-value of class type, so we need to
> +  // initialize a temporary.  For compatibility reasons, however, we
> +  // don't want to do this in unevaluated contexts; otherwise we
> +  // reject metaprograms which work by passing uncopyable l-values to
> +  // variadic functions.

4.1p2 of the C++11 FDIS says:

"When an lvalue-to-rvalue conversion occurs in an unevaluated operand or a 
subexpression thereof (Clause 5) the value contained in the referenced 
object is not accessed. Otherwise ...". 

C++03 is much less precise on the entire conversion wrt class types, but 
said if the expression occurs within the operand of a sizeof "the value 
contained in the referenced object is not accessed". I think the FDIS text 
will be a good reference to put on that comment.