[PATCH 1/2] libstdc++: Convert _RangeAdaptorClosure into a CRTP class [PR108827]
Jonathan Wakely
jwakely.gcc@gmail.com
Wed Aug 16 17:32:16 GMT 2023
On Wed, 16 Aug 2023 at 17:06, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> On Sun, Apr 16, 2023 at 11:24 PM Patrick Palka <ppalka@redhat.com> wrote:
> >
> > On Fri, 14 Apr 2023, Patrick Palka wrote:
> >
> > > Using the CRTP idiom for this base class avoids bloating the size of a
> > > pipeline when adding distinct empty range adaptor closure objects to it,
> > > as detailed in section 4.1 of P2387R3.
> > >
> > > But it means we can no longer define its operator| overloads as hidden
> > > friends, since each instantiation of _RangeAdaptorClosure would then
> > > introduce its own logically different hidden friends. So for example
> > > during overload resolution for the outer pipe operator in
> > >
> > > :x | (views::reverse | views::join)
> > >
> > > we'd have to consider 6 different hidden operator| friends:
> > >
> > > 2 from _RangeAdaptorClosure<_Reverse>
> > > 2 from _RangeAdaptorClosure<_Join>
> > > 2 from _RangeAdaptorClosure<_Pipe<_Reverse, _Join>>
> > >
> > > which is wasteful and can even cause hard errors in some cases. So we
> > > instead define the operator| overloads at namespace scope in an isolated
> > > namespace.
> >
> > On second thought, since this doesn't fix a bug or add new functionality
> > it seems more like GCC 14 material. The size reduction is nice but it's
> > probably not a big deal in practice since adaptor pipelines are usually
> > very transient objects that don't get passed around as function
> > arguments etc.
>
> Ping, does this look OK for trunk?
OK for trunk, thanks.
>
> >
> > But perhaps the second patch implementing range_adaptor_closure would be
> > desirable for GCC 13? I'll post an updated standalone version of that
> > patch for separate consideration.
> >
> > >
> > > PR libstdc++/108827
> > >
> > > libstdc++-v3/ChangeLog:
> > >
> > > * include/std/ranges (__adaptor::_RangeAdaptorClosure): Move ...
> > > (__adaptor::__closure::_RangeAdaptorClosure): ... here and turn
> > > it into a CRTP class template. Move hidden operator| friends
> > > into namespace scope and adjust their constraints. Add a
> > > using-declaration for this at __adaptor::_RangeAdaptorClosure.
> > > (__closure::__is_range_adaptor_closure_fn): Define.
> > > (__closure::__is_range_adaptor_closure): Define.
> > > (__adaptor::_Partial): Adjust use of _RangeAdaptorClosure.
> > > (__adaptor::_Pipe): Likewise.
> > > (views::_All): Likewise.
> > > (views::_Join): Likewise.
> > > (views::_Common): Likewise.
> > > (views::_Reverse): Likewise.
> > > (views::_Elements): Likewise.
> > > (views::_Adjacent): Likewise.
> > > (views::_AsRvalue): Likewise.
> > > (views::_Enumerate): Likewise.
> > > (views::_AsConst): Likewise.
> > > * testsuite/std/ranges/adaptors/all.cc: Reintroduce
> > > static_assert expecting that adding empty range adaptor
> > > closure objects to a pipeline doesn't increase the size of a
> > > pipeline.
> > > ---
> > > libstdc++-v3/include/std/ranges | 69 +++++++++++--------
> > > .../testsuite/std/ranges/adaptors/all.cc | 7 --
> > > 2 files changed, 42 insertions(+), 34 deletions(-)
> > >
> > > diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> > > index 283d757faa4..531ec6f68b3 100644
> > > --- a/libstdc++-v3/include/std/ranges
> > > +++ b/libstdc++-v3/include/std/ranges
> > > @@ -872,30 +872,45 @@ namespace views::__adaptor
> > > template<typename _Lhs, typename _Rhs>
> > > struct _Pipe;
> > >
> > > - // The base class of every range adaptor closure.
> > > - //
> > > - // The derived class should define the optional static data member
> > > - // _S_has_simple_call_op to true if the behavior of this adaptor is
> > > - // independent of the constness/value category of the adaptor object.
> > > - struct _RangeAdaptorClosure
> > > + namespace __closure
> > > {
> > > + // The base class of every range adaptor closure.
> > > + //
> > > + // The derived class should define the optional static data member
> > > + // _S_has_simple_call_op to true if the behavior of this adaptor is
> > > + // independent of the constness/value category of the adaptor object.
> > > + template<typename _Derived>
> > > + struct _RangeAdaptorClosure
> > > + { };
> > > +
> > > + template<typename _Tp, typename _Up>
> > > + requires (!same_as<_Tp, _RangeAdaptorClosure<_Up>>)
> > > + void __is_range_adaptor_closure_fn
> > > + (const _Tp&, const _RangeAdaptorClosure<_Up>&); // not defined
> > > +
> > > + template<typename _Tp>
> > > + concept __is_range_adaptor_closure
> > > + = requires (_Tp __t) { __closure::__is_range_adaptor_closure_fn(__t, __t); };
> > > +
> > > // range | adaptor is equivalent to adaptor(range).
> > > template<typename _Self, typename _Range>
> > > - requires derived_from<remove_cvref_t<_Self>, _RangeAdaptorClosure>
> > > + requires __is_range_adaptor_closure<_Self>
> > > && __adaptor_invocable<_Self, _Range>
> > > - friend constexpr auto
> > > + constexpr auto
> > > operator|(_Range&& __r, _Self&& __self)
> > > { return std::forward<_Self>(__self)(std::forward<_Range>(__r)); }
> > >
> > > // Compose the adaptors __lhs and __rhs into a pipeline, returning
> > > // another range adaptor closure object.
> > > template<typename _Lhs, typename _Rhs>
> > > - requires derived_from<_Lhs, _RangeAdaptorClosure>
> > > - && derived_from<_Rhs, _RangeAdaptorClosure>
> > > - friend constexpr auto
> > > + requires __is_range_adaptor_closure<_Lhs>
> > > + && __is_range_adaptor_closure<_Rhs>
> > > + constexpr auto
> > > operator|(_Lhs __lhs, _Rhs __rhs)
> > > { return _Pipe<_Lhs, _Rhs>{std::move(__lhs), std::move(__rhs)}; }
> > > - };
> > > + } // namespace __closure
> > > +
> > > + using __closure::_RangeAdaptorClosure;
> > >
> > > // The base class of every range adaptor non-closure.
> > > //
> > > @@ -937,7 +952,7 @@ namespace views::__adaptor
> > > // A range adaptor closure that represents partial application of
> > > // the range adaptor _Adaptor with arguments _Args.
> > > template<typename _Adaptor, typename... _Args>
> > > - struct _Partial : _RangeAdaptorClosure
> > > + struct _Partial : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>>
> > > {
> > > tuple<_Args...> _M_args;
> > >
> > > @@ -978,7 +993,7 @@ namespace views::__adaptor
> > > // A lightweight specialization of the above primary template for
> > > // the common case where _Adaptor accepts a single extra argument.
> > > template<typename _Adaptor, typename _Arg>
> > > - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure
> > > + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>>
> > > {
> > > _Arg _M_arg;
> > >
> > > @@ -1011,7 +1026,7 @@ namespace views::__adaptor
> > > template<typename _Adaptor, typename... _Args>
> > > requires __adaptor_has_simple_extra_args<_Adaptor, _Args...>
> > > && (is_trivially_copyable_v<_Args> && ...)
> > > - struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure
> > > + struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>>
> > > {
> > > tuple<_Args...> _M_args;
> > >
> > > @@ -1041,7 +1056,7 @@ namespace views::__adaptor
> > > template<typename _Adaptor, typename _Arg>
> > > requires __adaptor_has_simple_extra_args<_Adaptor, _Arg>
> > > && is_trivially_copyable_v<_Arg>
> > > - struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure
> > > + struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>>
> > > {
> > > _Arg _M_arg;
> > >
> > > @@ -1066,7 +1081,7 @@ namespace views::__adaptor
> > > // A range adaptor closure that represents composition of the range
> > > // adaptor closures _Lhs and _Rhs.
> > > template<typename _Lhs, typename _Rhs>
> > > - struct _Pipe : _RangeAdaptorClosure
> > > + struct _Pipe : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>>
> > > {
> > > [[no_unique_address]] _Lhs _M_lhs;
> > > [[no_unique_address]] _Rhs _M_rhs;
> > > @@ -1102,7 +1117,7 @@ namespace views::__adaptor
> > > template<typename _Lhs, typename _Rhs>
> > > requires __closure_has_simple_call_op<_Lhs>
> > > && __closure_has_simple_call_op<_Rhs>
> > > - struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure
> > > + struct _Pipe<_Lhs, _Rhs> : _RangeAdaptorClosure<_Pipe<_Lhs, _Rhs>>
> > > {
> > > [[no_unique_address]] _Lhs _M_lhs;
> > > [[no_unique_address]] _Rhs _M_rhs;
> > > @@ -1264,7 +1279,7 @@ namespace views::__adaptor
> > > concept __can_owning_view = requires { owning_view{std::declval<_Range>()}; };
> > > } // namespace __detail
> > >
> > > - struct _All : __adaptor::_RangeAdaptorClosure
> > > + struct _All : __adaptor::_RangeAdaptorClosure<_All>
> > > {
> > > template<typename _Range>
> > > static constexpr bool
> > > @@ -3048,7 +3063,7 @@ namespace views::__adaptor
> > > = requires { join_view<all_t<_Range>>{std::declval<_Range>()}; };
> > > } // namespace __detail
> > >
> > > - struct _Join : __adaptor::_RangeAdaptorClosure
> > > + struct _Join : __adaptor::_RangeAdaptorClosure<_Join>
> > > {
> > > template<viewable_range _Range>
> > > requires __detail::__can_join_view<_Range>
> > > @@ -3842,7 +3857,7 @@ namespace views::__adaptor
> > > = requires { common_view{std::declval<_Range>()}; };
> > > } // namespace __detail
> > >
> > > - struct _Common : __adaptor::_RangeAdaptorClosure
> > > + struct _Common : __adaptor::_RangeAdaptorClosure<_Common>
> > > {
> > > template<viewable_range _Range>
> > > requires __detail::__already_common<_Range>
> > > @@ -3963,7 +3978,7 @@ namespace views::__adaptor
> > > = requires { reverse_view{std::declval<_Range>()}; };
> > > } // namespace __detail
> > >
> > > - struct _Reverse : __adaptor::_RangeAdaptorClosure
> > > + struct _Reverse : __adaptor::_RangeAdaptorClosure<_Reverse>
> > > {
> > > template<viewable_range _Range>
> > > requires __detail::__is_reverse_view<remove_cvref_t<_Range>>
> > > @@ -4363,7 +4378,7 @@ namespace views::__adaptor
> > > } // namespace __detail
> > >
> > > template<size_t _Nm>
> > > - struct _Elements : __adaptor::_RangeAdaptorClosure
> > > + struct _Elements : __adaptor::_RangeAdaptorClosure<_Elements<_Nm>>
> > > {
> > > template<viewable_range _Range>
> > > requires __detail::__can_elements_view<_Nm, _Range>
> > > @@ -5484,7 +5499,7 @@ namespace views::__adaptor
> > > }
> > >
> > > template<size_t _Nm>
> > > - struct _Adjacent : __adaptor::_RangeAdaptorClosure
> > > + struct _Adjacent : __adaptor::_RangeAdaptorClosure<_Adjacent<_Nm>>
> > > {
> > > template<viewable_range _Range>
> > > requires (_Nm == 0) || __detail::__can_adjacent_view<_Nm, _Range>
> > > @@ -8609,7 +8624,7 @@ namespace views::__adaptor
> > > concept __can_as_rvalue_view = requires { as_rvalue_view(std::declval<_Tp>()); };
> > > }
> > >
> > > - struct _AsRvalue : __adaptor::_RangeAdaptorClosure
> > > + struct _AsRvalue : __adaptor::_RangeAdaptorClosure<_AsRvalue>
> > > {
> > > template<viewable_range _Range>
> > > requires __detail::__can_as_rvalue_view<_Range>
> > > @@ -8918,7 +8933,7 @@ namespace views::__adaptor
> > > = requires { enumerate_view<all_t<_Tp>>(std::declval<_Tp>()); };
> > > }
> > >
> > > - struct _Enumerate : __adaptor::_RangeAdaptorClosure
> > > + struct _Enumerate : __adaptor::_RangeAdaptorClosure<_Enumerate>
> > > {
> > > template<viewable_range _Range>
> > > requires __detail::__can_enumerate_view<_Range>
> > > @@ -9004,7 +9019,7 @@ namespace views::__adaptor
> > > concept __can_as_const_view = requires { as_const_view(std::declval<_Range>()); };
> > > }
> > >
> > > - struct _AsConst : __adaptor::_RangeAdaptorClosure
> > > + struct _AsConst : __adaptor::_RangeAdaptorClosure<_AsConst>
> > > {
> > > template<viewable_range _Range>
> > > constexpr auto
> > > diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
> > > index 57cb542174b..6bbaf73a20a 100644
> > > --- a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
> > > +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
> > > @@ -105,12 +105,6 @@ static_assert(std::is_empty_v<decltype(views::common
> > > | views::common
> > > | views::keys
> > > | views::reverse)>);
> > > -#if 0
> > > -// Adding empty range adaptor closure objects to a pipeline used to not
> > > -// increase the size of the pipeline, but now that our range adaptor closure
> > > -// objects derive from a common empty base class, [[no_unique_address]] can no
> > > -// longer make two empty adjacent range adaptor closure objects occupy the same
> > > -// data member address.
> > > static_assert(sizeof(decltype(views::take(5) | views::drop(5)))
> > > == sizeof(decltype(views::take(5)
> > > | views::join
> > > @@ -119,7 +113,6 @@ static_assert(sizeof(decltype(views::take(5) | views::drop(5)))
> > > | views::keys
> > > | views::drop(5)
> > > | views::reverse)));
> > > -#endif
> > >
> > > template<auto all = views::all>
> > > void
> > > --
> > > 2.40.0.335.g9857273be0
> > >
> > >
>
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