https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79138
Bug ID: 79138 Summary: ICE when trying to do template auto Product: gcc Version: 7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: barry.revzin at gmail dot com Target Milestone: --- The following example: #include <iostream> #include <type_traits> #include <utility> template <auto > struct value { }; template <auto... Vals> struct value_sequence { }; template <auto... As, auto... Bs> constexpr value_sequence<As..., Bs...> operator+(value_sequence<As...>, value_sequence<Bs...> ) { return {}; } template <auto Val, class F> constexpr auto filter_single(value<Val>, F predicate) { if constexpr (predicate(Val)) { return value_sequence<Val>{}; } else { return value_sequence<>{}; } } template <auto... Vals, class F> constexpr auto filter(value_sequence<Vals...>, F predicate) { return (filter_single(value<Vals>{}, predicate) + ...); } int main() { constexpr auto evens = filter( value_sequence<0, 1, 2, 3, 4, 5, 6, 7, 8, 9>{}, [](int i) constexpr { return i%2 == 0; }); } compiles on clang head, but on gcc head on wandbox, yields: prog.cc: In instantiation of 'constexpr auto filter_single(value<Val>, F) [with auto Val = 0; F = main()::<lambda(int)>]': prog.cc:30:26: required from 'constexpr auto filter(value_sequence<As ...>, F) [with auto ...Vals = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; F = main()::<lambda(int)>]' prog.cc:36:49: required from here prog.cc:21:36: internal compiler error: in tsubst, at cp/pt.c:13463 return value_sequence<Val>{}; ^ 0x618f06 tsubst(tree_node*, tree_node*, int, tree_node*) /home/heads/gcc/gcc-source/gcc/cp/pt.c:13463 0x61adb4 tsubst_template_args /home/heads/gcc/gcc-source/gcc/cp/pt.c:11625 0x627abc tsubst_aggr_type /home/heads/gcc/gcc-source/gcc/cp/pt.c:11837 0x618039 tsubst(tree_node*, tree_node*, int, tree_node*) /home/heads/gcc/gcc-source/gcc/cp/pt.c:13343 0x620909 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:17552 0x6150b7 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:16392 0x614e15 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:15656 0x614ee3 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:15870 0x615980 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:15840 0x614ee3 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:15870 0x61359a instantiate_decl(tree_node*, int, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:22797 0x64e093 maybe_instantiate_decl /home/heads/gcc/gcc-source/gcc/cp/decl2.c:5000 0x64f598 mark_used(tree_node*, int) /home/heads/gcc/gcc-source/gcc/cp/decl2.c:5099 0x5dcdb0 build_over_call /home/heads/gcc/gcc-source/gcc/cp/call.c:8074 0x5e1fbf build_new_function_call(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool, int) /home/heads/gcc/gcc-source/gcc/cp/call.c:4272 0x6beed1 finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool, bool, int) /home/heads/gcc/gcc-source/gcc/cp/semantics.c:2440 0x621d1f tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:17277 0x6150b7 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:16392 0x611b60 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool) /home/heads/gcc/gcc-source/gcc/cp/pt.c:15631 0x611b60 gen_elem_of_pack_expansion_instantiation /home/heads/gcc/gcc-source/gcc/cp/pt.c:10993