Am Do., 6. Feb. 2020 um 15:28 Uhr schrieb Jonathan Wakely <jwak...@redhat.com>: > > On 06/02/20 13:53 +0000, Jonathan Wakely wrote: > >On 06/02/20 13:40 +0000, Jonathan Wakely wrote: > >>This reduces sizeof(std::partial_ordering) and optimizes conversion and > >>comparison operators to avoid conditional branches where possible. > >> > >> * libsupc++/compare (__cmp_cat::_Ncmp::unordered): Change value to 2. > >> (partial_ordering::_M_is_ordered): Remove data member. > >> (partial_ordering): Use second bit of _M_value for unordered. Adjust > >> comparison operators. > >> (weak_ordering::operator partial_ordering): Simplify to remove > >> branches. > >> (operator<=>(unspecified, weak_ordering)): Likewise. > >> (strong_ordering::operator partial_ordering): Likewise. > >> (strong_ordering::operator weak_ordering): Likewise. > >> (operator<=>(unspecified, strong_ordering)): Likewise. > >> * testsuite/18_support/comparisons/categories/partialord.cc: New test. > >> * testsuite/18_support/comparisons/categories/strongord.cc: New test. > >> * testsuite/18_support/comparisons/categories/weakord.cc: New test. > >> > >>Tested powerpc64le-linux and x86_64-linux. > >> > >>This is an ABI change for the partial_ordering type, but that is why I > >>think we should do it now, not after GCC 10 is released. The sooner > >>the better, before these types are being widely used. > >> > >>I plan to commit this in the next 12 hours or so, unless there are > >>(valid :-) objections. > >> > >>Thanks to Barry Revzin for pointing out there was room for these > >>operators to be improved. > > > >We could also change the int _M_value data member of all three > >comparison category types to be a signed char instead of int. That > >would reduce the size further. > > Or maybe std::int_fast8_t is the right type here.
I like this suggestion. - Daniel
