On Mon, Feb 8, 2016 at 2:46 PM, H.J. Lu <hjl.to...@gmail.com> wrote: > On Mon, Feb 8, 2016 at 2:35 PM, Richard Smith <rich...@metafoo.co.uk> wrote: >> On Mon, Feb 8, 2016 at 1:40 PM, H.J. Lu <hjl.to...@gmail.com> wrote: >>> >>> On Mon, Feb 8, 2016 at 12:38 PM, Richard Smith <rich...@metafoo.co.uk> >>> wrote: >>> > On Mon, Feb 8, 2016 at 12:05 PM, H.J. Lu <hjl.to...@gmail.com> wrote: >>> >> >>> >> On Mon, Feb 8, 2016 at 11:33 AM, Jonathan Wakely <jwakely....@gmail.com> >>> >> wrote: >>> >> > On 8 February 2016 at 19:23, Richard Smith wrote: >>> >> >> "POD for the purpose of layout" is defined in the Itanium C++ ABI >>> >> >> here: >>> >> >> >>> >> >> http://mentorembedded.github.io/cxx-abi/abi.html#definitions >>> >> > >>> >> > Thanks. So there's no problem using "POD for the purposes of layout", >>> >> > and the change to "POD for the purpose of standard-layout" was >>> >> > unnecessary and just confused things. >>> >> >>> >> Here is the revised proposal: >>> >> >>> >> 1. "class type". A class type is a structure, union or C++ class. >>> >> 2. "empty class type". An empty class type is: >>> >> a. A class type without member. Or >>> >> b. A class type with only members of empty class types. Or >>> > >>> > >>> > (a) is a special case of (b). >>> > >>> >> c. An array of empty class types. >>> > >>> > >>> > It seems confusing to call an array a class type. Instead, how about: >>> > >>> > 2. An empty type is either an array of empty types or a class type where >>> > every member is of empty type. >>> > >>> >> 3. "empty record". An empty record is Plain Old Data (POD) for the >>> >> purposes of layout and >>> >> a. A class type without member. Or >>> >> b. A class type with only members of empty class types. >>> > >>> > >>> > (a) is a special case of (b). >>> > >>> >> 4. No memory slot nor register should be used to pass or return an object >>> >> of empty record. >>> > >>> > >>> > Objects of array type are never passed or returned (but if through some >>> > language extension they were, we'd want this rule to apply). So you don't >>> > need rule 3 and this can be just: >>> > >>> > 3. No memory slot nor register should be used to pass or return an object >>> > of empty type. >>> >>> Thanks very much for your inputs. Here is the proposal: >>> >>> 1. "class type". A class type is a structure, union or C++ class. >>> 2. "empty type". An empty type is either an array of empty types or a >>> class type where every member is of empty type. >>> 3. No memory slot nor register should be used to pass or return an object >>> of empty type. >> >> David Majnemer points out that we also need to say something about >> base classes. We could handle that case like this: >> >> 2. "empty type". An empty type is a type where it and all of its >> subobjects are of class or array type. >> >> Following the C++ rules, this also means that a class that contains >> only unnamed bitfields is empty, because unnamed bitfields are not >> subobjects, but might be worth explicitly stating for the C case. That >> also matches Clang's behavior. > > Like this? > > 1. "class type". A class type is a structure, union or C++ class. > 2. "empty type". An empty type is > a. A type where it and all of its subobjects are of class or array > type. And > b. Either an array of empty types or a class type where every member > is of empty type.
You don't need (b). It's implied by (a). > 3. No memory slot nor register should be used to pass or return an object > of empty type. > > > -- > H.J. _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
