On Mon, 15 Jan 2024 at 19:32, Patrick Palka <ppa...@redhat.com> wrote: > > On Sun, Jan 7, 2024 at 3:33 PM Patrick Palka <ppa...@redhat.com> wrote: > > > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk? > > Ping.
Huh, I thought I'd already approved this ... sorry. OK for trunk, with the -ftemplate-depth test change too. > > > > > -- >8 -- > > > > The recursively defined constraints on _Variadic_union's user-defined > > destructor (necessary for maintaining trivial destructibility of the > > variant iff all of its alternatives are) effectively require a template > > instantiation depth of 3x the number of variants, with the instantiation > > stack looking like > > > > ... > > _Variadic_union<B, C, ...> > > std::is_trivially_destructible_v<_Variadic_union<B, C, ...>> > > _Variadic_union<A, B, C, ...>::~_Variadic_union() > > _Variadic_union<A, B, C, ...> > > ... > > > > Ideally the template depth should be ~equal to the number of variants > > (plus a constant). Luckily it seems we don't need to compute trivial > > destructibility of the alternatives at all from _Variadic_union, since > > its only user _Variant_storage already has that information. To that > > end this patch removes these recursive constraints and instead passes > > this information down from _Variant_storage. After this patch, the > > template instantiation depth for 87619.cc is ~270 instead of ~780. > > > > libstdc++-v3/ChangeLog: > > > > * include/std/variant (__detail::__variant::_Variadic_union): > > Add bool __trivially_destructible template parameter. > > (__detail::__variant::_Variadic_union::~_Variadic_union): > > Use __trivially_destructible in constraints instead. > > (_Variant_storage): Pass __trivially_destructible value to > > _Variadic_union. > > --- > > libstdc++-v3/include/std/variant | 15 +++++++-------- > > 1 file changed, 7 insertions(+), 8 deletions(-) > > > > diff --git a/libstdc++-v3/include/std/variant > > b/libstdc++-v3/include/std/variant > > index 20a76c8aa87..4b9002e0917 100644 > > --- a/libstdc++-v3/include/std/variant > > +++ b/libstdc++-v3/include/std/variant > > @@ -392,7 +392,7 @@ namespace __variant > > }; > > > > // Defines members and ctors. > > - template<typename... _Types> > > + template<bool __trivially_destructible, typename... _Types> > > union _Variadic_union > > { > > _Variadic_union() = default; > > @@ -401,8 +401,8 @@ namespace __variant > > _Variadic_union(in_place_index_t<_Np>, _Args&&...) = delete; > > }; > > > > - template<typename _First, typename... _Rest> > > - union _Variadic_union<_First, _Rest...> > > + template<bool __trivially_destructible, typename _First, typename... > > _Rest> > > + union _Variadic_union<__trivially_destructible, _First, _Rest...> > > { > > constexpr _Variadic_union() : _M_rest() { } > > > > @@ -427,13 +427,12 @@ namespace __variant > > ~_Variadic_union() = default; > > > > constexpr ~_Variadic_union() > > - requires (!is_trivially_destructible_v<_First>) > > - || (!is_trivially_destructible_v<_Variadic_union<_Rest...>>) > > + requires (!__trivially_destructible) > > { } > > #endif > > > > _Uninitialized<_First> _M_first; > > - _Variadic_union<_Rest...> _M_rest; > > + _Variadic_union<__trivially_destructible, _Rest...> _M_rest; > > }; > > > > // _Never_valueless_alt is true for variant alternatives that can > > @@ -514,7 +513,7 @@ namespace __variant > > return this->_M_index != __index_type(variant_npos); > > } > > > > - _Variadic_union<_Types...> _M_u; > > + _Variadic_union<false, _Types...> _M_u; > > using __index_type = __select_index<_Types...>; > > __index_type _M_index; > > }; > > @@ -552,7 +551,7 @@ namespace __variant > > return this->_M_index != static_cast<__index_type>(variant_npos); > > } > > > > - _Variadic_union<_Types...> _M_u; > > + _Variadic_union<true, _Types...> _M_u; > > using __index_type = __select_index<_Types...>; > > __index_type _M_index; > > }; > > -- > > 2.43.0.254.ga26002b628 > > >