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

[H.J. Lu via cfe-commits]

On Mon, Feb 8, 2016 at 8:15 AM, Jonathan Wakely <jwakely.gcc at gmail.com> wrote:
> On 8 February 2016 at 16:05, H.J. Lu wrote:
>> My understanding is
>>
>> A type that is standard-layout means that it orders and packs its
>> members in a way that is compatible with C.
>>
>> What is the corresponding compatible type in C?
>
> An empty structure, such as struct A.
>
> One of the requirements for standard-layout classes is "has all
> non-static data members and bit-fields in the class and its base
> classes first declared in the same class" so standard layout classes
> are allowed to have base classes, as long as either the base class is
> empty (so doesn't alter layout) or the derived class doesn't add
> members (so has the same layout as the base). If neither the base
> class is an empty record, and the derived class doesn't add any
> non-static data members or bit-fields, then the base class should be
> an empty record too.

if it is the case

struct A { };
struct B { };
struct C : A, B { };

is an empty record.


-- 
H.J.