On Wed, 7 Feb 2024, Jonathan Wakely wrote: > > > On Wed, 7 Feb 2024 at 17:29, Patrick Palka <ppa...@redhat.com> wrote: > Tested on x86_64-pc-linux-gnu, does this look OK for trunk? > > > OK. > > Do we have a reduced testcase to track the modules bug that will still exist > in the FE?
https://gcc.gnu.org/PR113814 > > > > -- >8 -- > > The forward declarations of std::get in <bits/stl_pair.h> added in > r14-8710-g65b4cba9d6a9ff are causing an ICE in the test modules/hello-1 > due to what seems to be a declaration merging issue in modules. > > What seems to be happening is that in hello-1_b.C we first include > <string_view>, which indirectly includes <bits/stl_pair.h> which forms > the dependent specialization tuple_element<__i, tuple<_Elements...>> > (appearing in some of the std::get overloads) and adds it to the > specializations table. > > We then import hello which indirectly includes <tuple> (in the GMF), > within which we define a partial specialization of tuple_element with > that same template-id. So importing hello in turn streams in this > partial specialization, but we don't notice it matches the previously > created dependent specialization, and we end up with two equivalent > types for this template-id with different TYPE_CANONICAL. > > This patch works around this issue by adding a forward declaration of > the tuple_element partial specialization from <tuple> to > <bits/stl_pair.h> > so that it appears alongside the dependent specialization of the same > template-id. So when including <bits/stl_pair.h> we immediately > register > the template-id as a partial specialization, and if we later stream in > the > partial specialization the MK_partial case of trees_in::key_mergeable > will > match them up. (So perhaps a proper modules fix for this might be to > make > key_mergeable try to match up a streamed in partial specialization with > an > existing specialization from the table via > match_mergeable_specialization.) > > PR c++/113710 > > libstdc++-v3/ChangeLog: > > * include/bits/stl_pair.h (tuple_element): Add forward > declaration of the partial specialization for tuple. > --- > libstdc++-v3/include/bits/stl_pair.h | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/libstdc++-v3/include/bits/stl_pair.h > b/libstdc++-v3/include/bits/stl_pair.h > index 00ec53ebc33..8c71b1350e5 100644 > --- a/libstdc++-v3/include/bits/stl_pair.h > +++ b/libstdc++-v3/include/bits/stl_pair.h > @@ -1153,6 +1153,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > struct tuple_element<1, pair<_Tp1, _Tp2>> > { typedef _Tp2 type; }; > > + // Forward declare the partial specialization for std::tuple > + // to work around modules bug PR c++/113710. > + template<size_t __i, typename... _Types> > + struct tuple_element<__i, tuple<_Types...>>; > + > #if __cplusplus >= 201703L > template<typename _Tp1, typename _Tp2> > inline constexpr size_t tuple_size_v<pair<_Tp1, _Tp2>> = 2; > -- > 2.43.0.561.g235986be82 > > >
