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 7:02 AM, Jonathan Wakely <jwakely.gcc at gmail.com> wrote:
> On 8 February 2016 at 13:54, H.J. Lu <hjl.tools at gmail.com> wrote:
>> On Sun, Feb 7, 2016 at 12:52 PM, H.J. Lu <hjl.tools at gmail.com> wrote:
>>
>> The standard-layout POD is well defined:
>>
>> https://en.wikipedia.org/wiki/C%2B%2B11#Modification_to_the_definition_of_plain_old_data
>>
>> Here is the updated proposal for  Intel386, x86-64 and IA MCU psABIs:
>>
>> 1. "collection".  A collection is a structure, union or C++ class.
>
> These are all "class types". Why invent a new term?

Because it applies to both C and C++.  There is no class in C.

>> 2. "empty collection".  An empty collection is:
>>    a. A collection without member.  Or
>
> What about base classes?
>
> What about bit-fields of length 0?

Is a collection with them standard-layout POD type?

>>    b. A collection with only empty collections.  Or
>
> What does "with" mean? Only members, or bases too?

Is "A collection with only members of empty collections" better?

>>    c. An array of empty collections.
>> 3. "empty record".  An empty record is Plain Old Data (POD) for the purpose
>>    of standard-layout and
>
> "For the purposes of standard-layout" doesn't mean anything.
>
> A type is a standard-layout type, or it isn't.

How about "An empty record is standard-layout Plain Old Data (POD)
type and ..."?

> Do you mean "An empty record is a standard-layout type and..."
>
>>    a. A collection without member.  Or
>>    b. A collection with only empty collections.
>
> ?
>

Is "A collection with only members of empty collections" better?

>
>> 4. No memory slot nor register should be used to pass or return an object of
>> empty record.



-- 
H.J.