[Bug c++/60955] Erroneous warning about taking address of register with std=c++1y

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60955

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-04-26
                 CC|                            |manu at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Harald van Dijk from comment #2)
> This is caused by the implementation of C++1y decltype(auto), where
> seemingly redundant parentheses around an identifier must not simply be
> removed, because they may be significant.
> 
> int a;
> decltype(auto) b = a; // means int b = a;
> decltype(auto) c = (a); // means int &c = a;
> 
> GCC implements this by transforming (a) into static_cast<int &>(a)
> (force_paren_expr in gcc/cp/semantics.c), which would normally be a no-op,
> but causes the warning when a is declared using the "register" keyword.

It is pretty awful that C++14 has made extra parentheses to become significant.

But yes, this explains this bug and also PR57573.

It would be nice if expressions could be marked as compiler-generated, like we
have DECL_ARTIFICIAL for declarations. But you could set TREE_NO_WARNING(expr)
= true and check that in the warning code.