On Mon, Sep 14, 2020 at 11:13:18AM -0400, Jason Merrill via Gcc-patches wrote: > On Mon, Jun 29, 2020 at 1:25 PM Martin Liška <mli...@suse.cz> wrote: > > > > On 6/29/20 4:57 PM, Marek Polacek wrote: > > > On Mon, Jun 29, 2020 at 09:51:57AM +0200, Martin Liška wrote: > > >> On 6/26/20 9:34 PM, Marek Polacek via Gcc-patches wrote: > > >>> As discussed last month: > > >>> <https://gcc.gnu.org/pipermail/gcc-patches/2020-May/545879.html> > > >>> it's time to change the C++ default to gnu++17. I've committed the > > >>> patch after > > >>> testing x86_64-pc-linux-gnu and powerpc64le-unknown-linux-gnu. Brace > > >>> yourselves! > > >>> > > >>> Marek > > >>> > > >> > > >> Just a small note that 510.parest_r SPEC 2017 benchmark can't be built > > >> now > > >> with default changed to -std=c++17. The spec config needs to be adjusted. > > > > > > Interesting, do you know why? Does it use the register keyword? > > > > Apparently it needs -fno-new-ttp-matching for successful compilation. > > There's a reduced test-case I made: > > > > cat fe.ii > > template <int, int> class FiniteElement; > > template <int, int> class DoFHandler; > > class FETools { > > template <int dim, class InVector, class OutVector, int spacedim> > > void back_interpolate(const DoFHandler<dim, spacedim> &, const InVector > > &, > > const FiniteElement<dim, spacedim> &, OutVector &); > > template <int dim, template <int> class DH, class InVector, class > > OutVector, > > int spacedim> > > void back_interpolate(const DH<dim> &, InVector, > > const FiniteElement<dim, spacedim> &, OutVector); > > }; > > template <int dim, int = dim> class DoFHandler; > > template <int dim, int = dim> class FiniteElement; > > template <int dim, class InVector, class OutVector, int spacedim> > > void FETools::back_interpolate(const DoFHandler<dim, spacedim> &, > > const InVector &, > > const FiniteElement<dim, spacedim> &, > > OutVector &) {} > > template void FETools::back_interpolate(const DoFHandler<3> &, const float > > &, > > const FiniteElement<3> &, float &); > > Hmm, looks like I never sent this. > > Further reduced: > > template <int N, int M = N> class A; > template <int N, int M> void fn(A<N, M> &) {} > template <int N, template <int> class TT> void fn(TT<N> &); > template void fn(A<3> &); > > This breaks due to the C++17 changes to template template parameters > causing A to now be considered a valid argument for TT; with that > change both function templates are valid candidates, and neither is > more specialized than the other, so it's ambiguous. > > There are still some open core issues around these changes.
Thanks. I just pushed a patch to introduce GCC 11 porting_to: <https://gcc.gnu.org/gcc-11/porting_to.html> and documented this change. Let me know if you have any comments. Marek
