RFC: Update Intel386, x86-64 and IA MCU psABIs for passing/returning empty struct

[Michael Matz via cfe-commits]

Hi,

On Thu, 18 Feb 2016, H.J. Lu wrote:

> >> An empty type is a type where it and all of its subobjects 
> >> (recursively) are of class, structure, union, or array type.  No 
> >> memory slot nor register should be used to pass or return an object 
> >> of empty type.
> >
> > The trivially copyable is gone again.  Why is it not necessary?
> 
> I think we want to cover
> 
> struct
> {
>   unsigned int : 8;
> };
> 
> but not
> 
> struct
> {
>   unsigned int  i :8;
> };
> 
> " trivially copyable" applies to both.

Correct, but I'm not suggesting to use only the trivially copyable 
definition, I want to have it added as condition for not requiring a 
register or memory slot.  I.e. "an object of empty type that's trivially 
copyable".


Ciao,
Michael.