https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94628
--- Comment #8 from Martin Liška <marxin at gcc dot gnu.org> --- (In reply to Nicholas Krause from comment #7) > After adding this it seems to work for me, Patrick: > case TYPE_ARGUMENT_PACK: > if (value_dependent_expression_p(TREE_TYPE(*tp))) > return *tp; > if (TEMPLATE_TYPE_PARAMETER_PACK(*tp)) > return *tp; > return NULL_TREE; > > and gives me: > test.c: In function ‘std::common_type_t<decltype > (forward<F>(f)(std::integral_constant<int, i>(), > (forward<decltype(args)>)(args)...)), decltype > (forward<F>(f)(int_constant<Is>(), (forward<decltype(args)>)(args)...))...> > select(int, F&&, Args&& ...)’: > test.c:14:12: warning: ‘if constexpr’ only available with ‘-std=c++17’ or > ‘-std=gnu++17’ > 14 | if constexpr(sizeof...(Is)>0) > | ^~~~~~~~~ > test.c: In function ‘std::common_type_t<decltype > (forward<F>(f)(std::integral_constant<int, i>(), > (forward<decltype(select::args)>)(select::args)...)), decltype > (forward<F>(f)(int_constant<Is>(), > (forward<decltype(select::args)>)(select::args)...))...> select(int, F&&, > Args&& ...) [with int I = 1; int ...Is = {}; F = t(int)::<lambda(auto:1)>; > Args = {}]’: > test.c:17:1: warning: control reaches end of non-void function > [-Wreturn-type] > 17 | } > | ^ > > with no segfault. I'm not sure if this is the correct part to add this test > for TYPE_ARGUMENT_PACK or if we would prefer it to be lower in the stack. The suggested change is wrong: /home/marxin/Programming/gcc2/objdir/./gcc/xgcc -shared-libgcc -B/home/marxin/Programming/gcc2/objdir/./gcc -nostdinc++ -L/home/marxin/Programming/gcc2/objdir/x86_64-pc-linux-gnu/libstdc++-v3/src -L/home/marxin/Programming/gcc2/objdir/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs -L/home/marxin/Programming/gcc2/objdir/x86_64-pc-linux-gnu/libstdc++-v3/libsupc++/.libs -B/usr/local/x86_64-pc-linux-gnu/bin/ -B/usr/local/x86_64-pc-linux-gnu/lib/ -isystem /usr/local/x86_64-pc-linux-gnu/include -isystem /usr/local/x86_64-pc-linux-gnu/sys-include -x c++-header -nostdinc++ -g -O2 -D_GNU_SOURCE -I/home/marxin/Programming/gcc2/objdir/x86_64-pc-linux-gnu/libstdc++-v3/include/x86_64-pc-linux-gnu -I/home/marxin/Programming/gcc2/objdir/x86_64-pc-linux-gnu/libstdc++-v3/include -I/home/marxin/Programming/gcc2/libstdc++-v3/libsupc++ -O2 -g -std=gnu++0x /home/marxin/Programming/gcc2/libstdc++-v3/include/precompiled/stdc++.h \ -o x86_64-pc-linux-gnu/bits/stdc++.h.gch/O2ggnu++0x.gch In file included from /home/marxin/Programming/gcc2/objdir/x86_64-pc-linux-gnu/libstdc++-v3/include/cmath:42, from /home/marxin/Programming/gcc2/libstdc++-v3/include/precompiled/stdc++.h:41: /home/marxin/Programming/gcc2/objdir/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/cpp_type_traits.h:89:63: internal compiler error: tree check: expected template_type_parm or template_template_parm or bound_template_template_parm, have tree_list in instantiation_dependent_r, at cp/pt.c:26926 89 | enum { __value = bool(_Sp::__value) || bool(_Tp::__value) }; | ^ 0x8404c2 tree_check_failed(tree_node const*, char const*, int, char const*, ...) ../../gcc/tree.c:9727 0x69234b tree_check3(tree_node*, char const*, int, char const*, tree_code, tree_code, tree_code) ../../gcc/tree.h:3327 0x69234b instantiation_dependent_r ../../gcc/cp/pt.c:26926 0x13749b3 walk_tree_1(tree_node**, tree_node* (*)(tree_node**, int*, void*), void*, hash_set<tree_node*, false, default_hash_traits<tree_node*> >*, tree_node* (*)(tree_node**, int*, tree_node* (*)(tree_node**, int*, void*), void*, hash_set<tree_node*, false, default_hash_traits<tree_node*> >*)) ../../gcc/tree.c:11996 0xb10a88 cp_walk_subtrees(tree_node**, int*, tree_node* (*)(tree_node**, int*, void*), void*, hash_set<tree_node*, false, default_hash_traits<tree_node*> >*) ../../gcc/cp/tree.c:5061 0x1374a47 walk_tree_1(tree_node**, tree_node* (*)(tree_node**, int*, void*), void*, hash_set<tree_node*, false, default_hash_traits<tree_node*> >*, tree_node* (*)(tree_node**, int*, tree_node* (*)(tree_node**, int*, void*), void*, hash_set<tree_node*, false, default_hash_traits<tree_node*> >*)) ../../gcc/tree.c:12019 0x1377c85 walk_tree_without_duplicates_1(tree_node**, tree_node* (*)(tree_node**, int*, void*), void*, tree_node* (*)(tree_node**, int*, tree_node* (*)(tree_node**, int*, void*), void*, hash_set<tree_node*, false, default_hash_traits<tree_node*> >*)) ../../gcc/tree.c:12352 0xa97c87 instantiation_dependent_uneval_expression_p(tree_node*) ../../gcc/cp/pt.c:27033 0xa9e278 instantiation_dependent_expression_p(tree_node*) ../../gcc/cp/pt.c:27043 0x973ba7 is_nondependent_constant_expression(tree_node*) ../../gcc/cp/constexpr.c:8300 0x973fca fold_non_dependent_expr_template ../../gcc/cp/constexpr.c:6970 0xa98147 build_non_dependent_expr(tree_node*) ../../gcc/cp/pt.c:27531 0xb271ef build_x_binary_op(op_location_t const&, tree_code, tree_node*, tree_code, tree_node*, tree_code, tree_node**, int) ../../gcc/cp/typeck.c:4245 0xa54e71 cp_parser_binary_expression ../../gcc/cp/parser.c:9719 0xa5671e cp_parser_assignment_expression ../../gcc/cp/parser.c:9859 0xa556cd cp_parser_constant_expression ../../gcc/cp/parser.c:10153 0xa62028 cp_parser_enumerator_definition ../../gcc/cp/parser.c:19479 0xa62028 cp_parser_enumerator_list ../../gcc/cp/parser.c:19419 0xa62028 cp_parser_enum_specifier ../../gcc/cp/parser.c:19350 0xa62028 cp_parser_type_specifier ../../gcc/cp/parser.c:17680 Can you please next time send patch suggestion that at least survive GCC build?