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. 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
