* Jakub Jelinek:
> +@cindex @code{constexpr_only} function attribute
> +@item constexpr_only
> +The @code{constexpr_only} attribute can be applied to a @code{constexpr}
> function
> +declaration. When the function is defined, the function body is only used
> +for C++ constant evaluation purposes, otherwise the function definition is
> +treated as a external declaration. If the function is called or has its
> +address taken and such reference is not optimized away, external definition
> +without the attribute still needs to be provided in some other translation
> +units. When used on a @code{virtual constexpr} method, such a method can be
> +still a key method of the class. This attribute is intended mainly for
> +functions which were intentionally defined out of line in libraries for
> +optimization (e.g.@: because the function is very large), key method or ABI
> +reasons but later on are required or desirable to be evaluable in constant
> +expressions.
Does this mean that no IPA is performed with the knowledge of the body?
ABI-wise, how does this interact with compilers that do not support
the attribute if it is used in the intended way? Can the function
still be made constexpr for those compilers?
