[Bug c++/115195] New: [12 Regression] Segfault when instantiating template

["patrick at rivosinc dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115195

            Bug ID: 115195
           Summary: [12 Regression] Segfault when instantiating template
           Product: gcc
           Version: 12.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick at rivosinc dot com
  Target Milestone: ---

Testcase:
enum a { b };
using c = int;
template <typename d> void e(int, int, int, c *, d, int) {
  [](auto) {
    [] {
      struct {
      } f;
    };
  };
}
int g, h;
a i() {
  return b;
  e({}, {}, g, &h, [] {}, {});
}

Backtrace (from godbolt since it's more verbose than my local backtrace):
> g++-12 reduced.cc
<source>: In instantiation of 'void e(int, int, int, c*, d, int) [with d =
i()::<lambda()>; c = int]':
<source>:14:4:   required from here
<source>:5:5: internal compiler error: Segmentation fault
    5 |     [] {
      |     ^
0x1bbabfe internal_error(char const*, ...)
        ???:0
0x10b0223 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*> >*))
        ???:0
0x10b0516 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*> >*))
        ???:0
0x10b0223 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*> >*))
        ???:0
0x870a79 check_for_bare_parameter_packs(tree_node*, unsigned int)
        ???:0
0x8a7dfb finish_expr_stmt(tree_node*)
        ???:0
0x891a08 tsubst_lambda_expr(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x87e337 instantiate_decl(tree_node*, bool, bool)
        ???:0
0x899e8b instantiate_pending_templates(int)
        ???:0
0x7a5298 c_parse_final_cleanups()
        ???:0
Please submit a full bug report, with preprocessed source.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.

Godbolt: https://godbolt.org/z/dda478Po6

Only on GCC 12.