https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119732
--- Comment #1 from Matthias Kretz (Vir) <mkretz at gcc dot gnu.org> --- After rebuilding GCC with checking enabled I get the following trace: constexpr.core2.ii: In instantiation of ‘array convert_mask() [with _Tp = array]’: constexpr.core2.ii:10:22: required from here 10 | convert_mask<array>(); | ~~~~~~~~~~~~~~~~~~~^~ constexpr.core2.ii:5:66: internal compiler error: in tsubst_pack_expansion, at cp/pt.cc:13924 5 | return {[]<int... _Js> { Impl0_convert_mask<_Tp>(_Js); }()...}; | ^ 0x298a05f internal_error(char const*, ...) /home/mkretz/src/gcc-master/gcc/diagnostic-global-context.cc:517 0xaf4ee3 fancy_abort(char const*, int, char const*) /home/mkretz/src/gcc-master/gcc/diagnostic.cc:1749 0x8a0699 tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*) /home/mkretz/src/gcc-master/gcc/cp/pt.cc:13924 0xd5c4f9 tsubst_expr(tree_node*, tree_node*, int, tree_node*) /home/mkretz/src/gcc-master/gcc/cp/pt.cc:21856 0xd49ee0 tsubst_stmt /home/mkretz/src/gcc-master/gcc/cp/pt.cc:20012 0xd4b8b4 tsubst_stmt /home/mkretz/src/gcc-master/gcc/cp/pt.cc:18875 0xd4c5a1 tsubst_stmt /home/mkretz/src/gcc-master/gcc/cp/pt.cc:18865 0xd4acb6 tsubst_stmt /home/mkretz/src/gcc-master/gcc/cp/pt.cc:19230 0xd73a56 tsubst_stmt /home/mkretz/src/gcc-master/gcc/cp/pt.cc:18851 0xd73a56 instantiate_body /home/mkretz/src/gcc-master/gcc/cp/pt.cc:27729 0xd49acc instantiate_decl(tree_node*, bool, bool) /home/mkretz/src/gcc-master/gcc/cp/pt.cc:28013 0xd83aeb instantiate_pending_templates(int) /home/mkretz/src/gcc-master/gcc/cp/pt.cc:28090 0xc03562 c_parse_final_cleanups() /home/mkretz/src/gcc-master/gcc/cp/decl2.cc:5571 0xe812f0 c_common_parse_file() /home/mkretz/src/gcc-master/gcc/c-family/c-opts.cc:1397