https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91377
--- Comment #2 from Jeffrey Kelling <gcc.j.kelling at hzdr dot de> --- Created attachment 46680 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46680&action=edit gcc 7.3.0 preprocessed source Not sure if it helps, but here is the code preprocessed by gcc 7.3.0. This compiles with gcc 7.3.0. gcc 9.1.0 does not like this one: ./thirdParty/alpaka/include/alpaka/vec/Vec.hpp: In instantiation of ‘decltype (createVecFromIndexedFnArbitrary<TDim, template<long unsigned int <anonymous> > class TTFnObj>(alpaka::meta::MakeIntegerSequence<typename TDim::value_type, TDim::value>(), (forward<TArgs>)(alpaka::vec::createVecFromIndexedFn::args)...)) alpaka::vec::createVecFromIndexedFn(TArgs&& ...) [with TDim = std::integral_constant<long unsigned int, 3>; TTFnObj = alpaka::vec::Vec<std::integral_constant<long unsigned int, 3>, unsigned int>::CreateSingleVal; TArgs = {const unsigned int&}]’: include/picongpu/main.cpp:70:1: required from here ./thirdParty/alpaka/include/alpaka/vec/Vec.hpp:99:14: sorry, unimplemented: mangling implicit_conv_expr
