[Bug c++/85028] New: ICE on invalid C++ code: in tsubst_default_argument, at cp/pt.c:12340

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85028

            Bug ID: 85028
           Summary: ICE on invalid C++ code: in tsubst_default_argument,
                    at cp/pt.c:12340
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

It appears to be a recent regression. 

$ g++tk -v
Using built-in specs.
COLLECT_GCC=g++tk
COLLECT_LTO_WRAPPER=/home/su/software/tmp/gcc/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/8.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/home/su/software/tmp/gcc/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 8.0.1 20180321 (experimental) [trunk revision 258722] (GCC)
$ 
$ g++tk tmp.cpp
tmp.cpp:7:11: error: ‘<anonymous>’ has incomplete type
   B (int, A = A()) : f (0) {}
           ^~~~~~~
tmp.cpp:3:8: note: forward declaration of ‘struct A’
 struct A;
        ^
tmp.cpp:11:15: internal compiler error: in tsubst_default_argument, at
cp/pt.c:12340
 B < int > b (0);
               ^
0x8676bf tsubst_default_argument(tree_node*, int, tree_node*, tree_node*, int)
        ../../gcc-source-trunk/gcc/cp/pt.c:12340
0x6c9907 convert_default_arg(tree_node*, tree_node*, tree_node*, int, int)
        ../../gcc-source-trunk/gcc/cp/call.c:7347
0x6ca4d8 build_over_call
        ../../gcc-source-trunk/gcc/cp/call.c:7974
0x6d8bfc build_new_method_call_1
        ../../gcc-source-trunk/gcc/cp/call.c:9343
0x6d8bfc build_new_method_call(tree_node*, tree_node*, vec<tree_node*, va_gc,
vl_embed>**, tree_node*, int, tree_node**, int)
        ../../gcc-source-trunk/gcc/cp/call.c:9419
0x6d9d43 build_special_member_call(tree_node*, tree_node*, vec<tree_node*,
va_gc, vl_embed>**, tree_node*, int, int)
        ../../gcc-source-trunk/gcc/cp/call.c:8949
0x7b55f0 expand_default_init
        ../../gcc-source-trunk/gcc/cp/init.c:1893
0x7b55f0 expand_aggr_init_1
        ../../gcc-source-trunk/gcc/cp/init.c:2007
0x7b63e4 build_aggr_init(tree_node*, tree_node*, int, int)
        ../../gcc-source-trunk/gcc/cp/init.c:1748
0x752d6c build_aggr_init_full_exprs
        ../../gcc-source-trunk/gcc/cp/decl.c:6271
0x752d6c check_initializer
        ../../gcc-source-trunk/gcc/cp/decl.c:6420
0x77b369 cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int)
        ../../gcc-source-trunk/gcc/cp/decl.c:7125
0x8384fd cp_parser_init_declarator
        ../../gcc-source-trunk/gcc/cp/parser.c:19740
0x83a1bf cp_parser_simple_declaration
        ../../gcc-source-trunk/gcc/cp/parser.c:13065
0x83b108 cp_parser_block_declaration
        ../../gcc-source-trunk/gcc/cp/parser.c:12883
0x847034 cp_parser_declaration
        ../../gcc-source-trunk/gcc/cp/parser.c:12780
0x8459b6 cp_parser_declaration_seq_opt
        ../../gcc-source-trunk/gcc/cp/parser.c:12656
0x845cd3 cp_parser_translation_unit
        ../../gcc-source-trunk/gcc/cp/parser.c:4561
0x845cd3 c_parse_file()
        ../../gcc-source-trunk/gcc/cp/parser.c:39017
0x98fe15 c_common_parse_file()
        ../../gcc-source-trunk/gcc/c-family/c-opts.c:1132
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
$


---------------------------------


// should have been:
// struct A {};
struct A;

template < typename > struct B
{ 
  B (int, A = A()) : f (0) {}
  int f;
};

B < int > b (0);