[Bug c++/97096] New: ICE on invalid: in register_constexpr_fundef, on out-of-line-defaulted operator== or operator<=>

[arthur.j.odwyer at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97096

            Bug ID: 97096
           Summary: ICE on invalid: in register_constexpr_fundef, on
                    out-of-line-defaulted operator== or operator<=>
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arthur.j.odwyer at gmail dot com
  Target Milestone: ---

// https://godbolt.org/z/neqx1q

cat >test.cpp <<EOF
namespace std {
    class strong_ordering {
        static const strong_ordering less;
        static const strong_ordering equal;
        static const strong_ordering equivalent;
        static const strong_ordering greater;
    };
}

struct S {
    friend bool operator==(S, S) = default;
};
bool operator==(S, S) noexcept = default;
EOF
g++ -std=c++20 test.cpp

test.cpp: In function 'constexpr bool operator==(S, S)':
test.cpp:13:6: internal compiler error: in register_constexpr_fundef, at
cp/constexpr.c:932
   14 | bool operator==(S, S) noexcept = default;
      |      ^~~~~~~~
0x1b74f49 internal_error(char const*, ...)
        ???:0
0x686ceb fancy_abort(char const*, int, char const*)
        ???:0
0x6f7903 register_constexpr_fundef(tree_node*, tree_node*)
        ???:0
0x7799a7 finish_function(bool)
        ???:0
0x7f1d8b synthesize_method(tree_node*)
        ???:0
0x77cf76 cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int)
        ???:0
0x862bdc c_parse_file()
        ???:0
0x9d34f2 c_common_parse_file()
        ???:0
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.


The same ICE happens if you replace both instances of `==` with `<=>`.