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

[H.J. Lu via cfe-commits]

On Sat, Feb 20, 2016 at 9:47 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On 20 Feb 2016 6:54 p.m., "H.J. Lu" <hjl.tools at gmail.com> wrote:
>>
>> On Sat, Feb 20, 2016 at 4:57 PM, Matthijs van Duin
>> <matthijsvanduin at gmail.com> wrote:
>> > On 20 February 2016 at 23:35, H.J. Lu <hjl.tools at gmail.com> wrote:
>> >> Can a compiler tell if a copy constructor or destructor is trivial
>> >> from the class declaration without function body?
>> >
>> > Yes, the mere presence of the declaration suffices to render it
>> > non-trivial (unless explicitly declared "= default" like I did with
>> > the default constructor, in which case there's no function body).
>>
>> How about this?
>>
>> An empty type is a type where it and all of its subobjects (recursively)
>> are of class, structure, union, or array type.  An empty type may only
>> have static member functions, default  constructor, default copy
>> constructor, default copy assignment operator or default destructor.
>
> No, that's the wrong rule still. Please leave the C++ rule here to the C++
> ABI rather than trying to reinvent it. Whether a type is empty is completely
> orthogonal to whether it must be passed through memory for C++ ABI /
> semantics reasons.

What is the correct wording?  The last one:

An empty type is a type where it and all of its subobjects (recursively)
are of class, structure, union, or array type.

doesn't cover "trivially-copyable".

-- 
H.J.