[Bug c++/71220] New: ICE on instantiation using variadic template

["rippey.e at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71220

            Bug ID: 71220
           Summary: ICE on instantiation using variadic template
           Product: gcc
           Version: 6.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rippey.e at gmail dot com
  Target Milestone: ---

Running g++ 6.1.0 on the following code:

struct S1{};

template<typename,typename>
template<typename...>
using U=S1;

template<typename>
struct S2{
        template<typename,typename=U<>>
        struct S3;
        S3<S1>
};

produces this error message:

a1.cpp:11:7: internal compiler error: Segmentation fault
  S3<S1>
       ^
0xaf5d8f crash_signal
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/toplev.c:333
0x63d839 tsubst(tree_node*, tree_node*, int, tree_node*)
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/pt.c:12968
0x643f42 tsubst_template_args
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/pt.c:11221
0x644042 tsubst_template_args
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/pt.c:11181
0x63d969 tsubst(tree_node*, tree_node*, int, tree_node*)
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/pt.c:13218
0x63de32 tsubst(tree_node*, tree_node*, int, tree_node*)
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/pt.c:12841
0x643674 coerce_template_parms
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/pt.c:7687
0x643def coerce_innermost_template_parms
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/pt.c:7803
0x644849 lookup_template_class_1
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/pt.c:8294
0x644849 lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*,
int, int)
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/pt.c:8638
0x6db2fd finish_template_type(tree_node*, tree_node*, int)
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/semantics.c:3154
0x69a316 cp_parser_template_id
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/parser.c:14914
0x69a48b cp_parser_class_name
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/parser.c:21201
0x68e3b9 cp_parser_qualifying_entity
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/parser.c:6237
0x68e3b9 cp_parser_nested_name_specifier_opt
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/parser.c:5923
0x69bd1f cp_parser_nested_name_specifier
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/parser.c:6167
0x69bd1f cp_parser_using_declaration
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/parser.c:17743
0x6a67d7 cp_parser_member_declaration
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/parser.c:22294
0x6892a1 cp_parser_member_specification_opt
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/parser.c:22154
0x6892a1 cp_parser_class_specifier_1
        /disk/0/erippey/gcc/objdir/../gcc-6.1.0/gcc/cp/parser.c:21346
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