On Wed, Mar 16, 2016 at 7:33 AM, Jason Merrill <ja...@redhat.com> wrote: > On 03/16/2016 07:55 AM, H.J. Lu wrote: >> >> On Tue, Mar 15, 2016 at 7:51 PM, Jason Merrill <ja...@redhat.com> wrote: >>> >>> On 03/15/2016 08:25 PM, Joseph Myers wrote: >>>> >>>> >>>> On Tue, 15 Mar 2016, H.J. Lu wrote: >>>> >>>>> On Tue, Mar 15, 2016 at 3:34 PM, Joseph Myers <jos...@codesourcery.com> >>>>> wrote: >>>>>> >>>>>> >>>>>> On Tue, 15 Mar 2016, H.J. Lu wrote: >>>>>> >>>>>>> On Tue, Mar 15, 2016 at 2:39 PM, Joseph Myers >>>>>>> <jos...@codesourcery.com> >>>>>>> wrote: >>>>>>>> >>>>>>>> >>>>>>>> I'm not sure if the zero-size arrays (a GNU extension) are >>>>>>>> considered >>>>>>>> to >>>>>>>> make a struct non-empty, but in any case I think the tests should >>>>>>>> cover >>>>>>>> such arrays as elements of structs. >>>>>>> >>>>>>> >>>>>>> >>>>>>> There are couple tests for structs with members of array >>>>>>> of empty types. testsuite/g++.dg/abi/empty14.h has >>>>>> >>>>>> >>>>>> >>>>>> My concern is the other way round - structs with elements such as >>>>>> "int a[0];", an array [0] of a nonempty type. My reading of the >>>>>> subobject >>>>>> definition is that such an array should not cause the struct to be >>>>>> considered nonempty (it doesn't result in any int subobjects). >>>>> >>>>> >>>>> >>>>> This is a test for struct with zero-size array, which isn't treated >>>>> as empty type. C++ and C are compatible in its passing. >>>> >>>> >>>> >>>> Where is the current definition of empty types you're proposing for use >>>> in >>>> GCC? Is the behavior of this case clear from that definition? >>> >>> >>> >>> "An empty type is a type where it and all of its subobjects (recursively) >>> are of structure, union, or array type. No memory slot nor register >>> should >>> be used to pass or return an object of empty type." >>> >>> It seems to me that such a struct should be considered an empty type >>> under >>> this definition, since a zero-length array has no subobjects. >> >> >> Since zero-size array is GCC extension, we can change it. Do we >> want to change its passing for C? > > > I would think so; it seems to follow clearly from this definition. I have > trouble imagining that anyone would ever pass an object containing a > zero-length array by value, so it shouldn't matter much either way, but I > consistency is good. >
This requires change in both C and C++ frontends. -- H.J.