https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71833
Bug ID: 71833 Summary: ICE on valid C++11 code with nested variadic templates: tree check: accessed elt 0 of tree_vec with 1 elts in coerce_template_parameter_pack, at cp/pt.c:7439 Product: gcc Version: 7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: su at cs dot ucdavis.edu Target Milestone: --- The following C++11 code causes an ICE when compiled with the current GCC trunk on x86_64-linux-gnu in both 32-bit and 64-bit modes. It is a regression from 6.1.x, but which (and earlier versions of GCC) incorrectly rejects the code. $ g++-trunk -v Using built-in specs. COLLECT_GCC=g++-trunk COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto --prefix=/usr/local/gcc-trunk --disable-bootstrap Thread model: posix gcc version 7.0.0 20160710 (experimental) [trunk revision 238196] (GCC) $ $ clang++-3.8 -c -std=c++11 small.cpp $ $ g++-6.1 -c -std=c++11 small.cpp small.cpp:6:15: error: wrong number of template arguments (0, should be 1) A <>::B < int > e; ^ $ $ g++-trunk -c -std=c++11 small.cpp small.cpp:6:15: internal compiler error: tree check: accessed elt 0 of tree_vec with 1 elts in coerce_template_parameter_pack, at cp/pt.c:7439 A <>::B < int > e; ^ 0x10666c5 tree_vec_elt_check_failed(int, int, char const*, int, char const*) ../../gcc-source-trunk/gcc/tree.c:9948 0x6fb4c0 tree_vec_elt_check ../../gcc-source-trunk/gcc/tree.h:3251 0x6fb4c0 coerce_template_parameter_pack ../../gcc-source-trunk/gcc/cp/pt.c:7439 0x6fb4c0 coerce_template_parms ../../gcc-source-trunk/gcc/cp/pt.c:7659 0x6fbf29 coerce_innermost_template_parms ../../gcc-source-trunk/gcc/cp/pt.c:7840 0x6fd7ea lookup_template_class_1 ../../gcc-source-trunk/gcc/cp/pt.c:8331 0x6fd7ea lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*, int, int) ../../gcc-source-trunk/gcc/cp/pt.c:8672 0x81769d finish_template_type(tree_node*, tree_node*, int) ../../gcc-source-trunk/gcc/cp/semantics.c:3133 0x7a3ce4 cp_parser_template_id ../../gcc-source-trunk/gcc/cp/parser.c:14919 0x7a3f8a cp_parser_class_name ../../gcc-source-trunk/gcc/cp/parser.c:21223 0x7929ad cp_parser_qualifying_entity ../../gcc-source-trunk/gcc/cp/parser.c:6250 0x7929ad cp_parser_nested_name_specifier_opt ../../gcc-source-trunk/gcc/cp/parser.c:5934 0x7a4707 cp_parser_constructor_declarator_p ../../gcc-source-trunk/gcc/cp/parser.c:25148 0x7a4707 cp_parser_decl_specifier_seq ../../gcc-source-trunk/gcc/cp/parser.c:12748 0x7adc91 cp_parser_simple_declaration ../../gcc-source-trunk/gcc/cp/parser.c:12304 0x7ae0e1 cp_parser_block_declaration ../../gcc-source-trunk/gcc/cp/parser.c:12251 0x7b6d50 cp_parser_declaration ../../gcc-source-trunk/gcc/cp/parser.c:12148 0x7b5824 cp_parser_declaration_seq_opt ../../gcc-source-trunk/gcc/cp/parser.c:12027 0x7b5b58 cp_parser_translation_unit ../../gcc-source-trunk/gcc/cp/parser.c:4329 0x7b5b58 c_parse_file() ../../gcc-source-trunk/gcc/cp/parser.c:37505 Please submit a full bug report, with preprocessed source if appropriate. Please include the complete backtrace with any bug report. See <http://gcc.gnu.org/bugs.html> for instructions. $ ----------------------------------------------------- template < typename ... Ts > struct A { template < Ts ..., typename ... Us > struct B {}; }; A <>::B < int > e;