[Bug c++/85043] -Wuseless-cast false positive for temporary objects

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85043

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #4)
> Why would user-provided copy ctor matter?  In this testcase there is no
> user-provided copy ctor, what matters is that the static cast is handled
> through
> perform_direct_initialization_if_possible as direct initialization of a
> temporary, without the cast there is no temporary.
> 
> -Wuseless-cast complains about all these below, and none of the casts are
> useless, all of them create a temporary.  So perhaps not warn at all if
> CLASS_TYPE_P (type)?

Yes I suppose you're right. For a non-class type all operators that modify the
operand also have non-modifying forms, i.e. ++i can be replaced by (i + 1), and
i+=n can be replaced with i+n, so there's no need to perform a useless cast to
create a temporary. So creatinga not-useless temporary is only necessary for
class types.