On Tue, Jan 26, 2016 at 12:23 PM, Marc Glisse <marc.gli...@inria.fr> wrote: > On Tue, 26 Jan 2016, H.J. Lu wrote: > >> On Tue, Jan 26, 2016 at 11:27 AM, Jason Merrill <ja...@redhat.com> wrote: >>> >>> On 12/14/2015 05:08 PM, H.J. Lu wrote: >>>> >>>> >>>> + if (abi_version_at_least (10)) >>>> + TYPE_EMPTY_RECORD (t) = is_really_empty_class (t); >>> >>> >>> >>> This should use is_empty_class or CLASSTYPE_EMPTY_P. We don't want to >>> change how classes with just a vptr are passed. >>> >>> Otherwise, it looks OK to me. >> >> >> Is true_type an empty class here? is_empty_class returns false >> on this: > > > It isn't empty in the usual C++ sense (we can't apply the empty base > optimization to something that derives from it, for instance), or the one > described in the itanium ABI (the relevant one here I guess). On the other > hand, it is rather useless to pass it by value, so a different notion of
llvm/clang treats it as empty class and I think it should be treated as "empty" class. > empty might have been useful when the ABI was defined... I proposed to update x86-64 psABI: https://groups.google.com/forum/#!topic/x86-64-abi/VTE-LJ9VnDk > >> [hjl@gnu-skl-1 gcc]$ cat x.cc >> struct dummy { }; >> struct true_type { struct dummy i; }; >> >> extern true_type y; >> extern void xxx (true_type c); >> >> void >> yyy (void) >> { >> xxx (y); >> } >> [hjl@gnu-skl-1 gcc]$ > > > -- > Marc Glisse -- H.J.
