[cxx-abi-dev] Passing an empty class by value

[Gabriel Dos Reis]

Passing nothing at all is makes the most sense for a vigorous C++ support.
Passing a 1-byte that nothing can possibly read and makes sense of is an
unfortunate sub-optimal codegen.

On Thu, Dec 10, 2015 at 11:05 PM, Marc Glisse <marc.glisse at inria.fr> wrote:

> On Fri, 11 Dec 2015, Nelson, Clark wrote:
>
> It has come to my attention that GCC and clang generate incompatible code
>> for passing an argument of an empty class type.
>>
>> clang seems to completely ignore arguments and parameters of empty class
>> type -- which seems to make a certain amount of sense.
>>
>> OTOH, as far as I understand it, GCC effectively treats an empty class
>> equivalently to a class containing a single member with some character
>> type -- which also seems pretty reasonable.
>>
>> Should the C++ ABI come down on one side or the other of this question?
>>
>
> See A-5 in https://mentorembedded.github.io/cxx-abi/cxx-closed.html for
> some historical discussion.
>
> This is really the sort of question a psABI should settle. But of course
>> the C language doesn't actually support a structure with no members, so
>> it's not too surprising if a psABI doesn't nail down what should happen
>> for this.
>>
>
> Last time I raised this, psABI was also suggested:
> http://sourcerytools.com/pipermail/cxx-abi-dev/2013-November/002627.html
>
> --
> Marc Glisse
>
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