[Bug c++/101886] New: [11/12 Regression][concepts] ICE with auto as template parameter

["reichelt at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

            Bug ID: 101886
           Summary: [11/12 Regression][concepts] ICE with auto as template
                    parameter
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: reichelt at gcc dot gnu.org
  Target Milestone: ---

The following valid code snippet (compiled with "-fconcepts")
triggers an ICE since GCC 11.1.0:

========================================
template<typename...> struct A { };

A<int, int> a;
A<auto, auto> b1 = a;
A<auto, auto> b2 = a;
========================================

bug.cc:5:13: internal compiler error: same canonical type node for different
types 'auto' and 'auto'
    5 | A<auto, auto> b2 = a;
      |             ^
0xb4eb9d comptypes(tree_node*, tree_node*, int)
        ../../gcc-11.1.0/gcc/cp/typeck.c:1565
0xab322f template_args_equal(tree_node*, tree_node*, bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9231
0xb42e41 cp_tree_equal(tree_node*, tree_node*)
        ../../gcc-11.1.0/gcc/cp/tree.c:4079
0xab305a template_args_equal(tree_node*, tree_node*, bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9249
0xab2d88 template_args_equal(tree_node*, tree_node*, bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9194
0xab2d88 comp_template_args(tree_node*, tree_node*, tree_node**, tree_node**,
bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9278
0xab2d88 comp_template_args(tree_node*, tree_node*, tree_node**, tree_node**,
bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9258
0xabc9f3 spec_hasher::equal(spec_entry*, spec_entry*)
        ../../gcc-11.1.0/gcc/cp/pt.c:1727
0xb02944 hash_table<spec_hasher, false,
xcallocator>::find_with_hash(spec_entry* const&, unsigned int)
        ../../gcc-11.1.0/gcc/hash-table.h:923
0xaeef47 lookup_template_class_1
        ../../gcc-11.1.0/gcc/cp/pt.c:9889
0xaf0bfc lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*,
int, int)
        ../../gcc-11.1.0/gcc/cp/pt.c:10244
0xb1914b finish_template_type(tree_node*, tree_node*, int)
        ../../gcc-11.1.0/gcc/cp/semantics.c:3581
0xa8a8eb cp_parser_template_id
        ../../gcc-11.1.0/gcc/cp/parser.c:17486
0xa8aadb cp_parser_class_name
        ../../gcc-11.1.0/gcc/cp/parser.c:24722
0xa81fda cp_parser_qualifying_entity
        ../../gcc-11.1.0/gcc/cp/parser.c:7002
0xa81fda cp_parser_nested_name_specifier_opt
        ../../gcc-11.1.0/gcc/cp/parser.c:6684
0xaa2e18 cp_parser_template_introduction
        ../../gcc-11.1.0/gcc/cp/parser.c:30254
0xaa50c3 cp_parser_declaration
        ../../gcc-11.1.0/gcc/cp/parser.c:14149
0xaa5e4c cp_parser_toplevel_declaration
        ../../gcc-11.1.0/gcc/cp/parser.c:14183
0xaa5e4c cp_parser_translation_unit
        ../../gcc-11.1.0/gcc/cp/parser.c:4942
Please submit a full bug report, [etc.]