I was playing around with the spaceship operator using gcc10 on godbolt and discovered an issue trying to compile the following program: struct Basics { int i; char c; float f; double d; auto operator<=>(const Basics&) const = default; }; struct Arrays { int ai[1]; char ac[2]; float af[3]; double ad[2][2]; auto operator<=>(const Arrays&) const = default; }; struct Bases : Basics, Arrays { auto operator<=>(const Bases&) const = default; }; int main() { constexpr Bases a = { { 0, 'c', 1.f, 1. }, { { 1 }, { 'a', 'b' }, { 1.f, 2.f, 3.f }, { { 1., 2. }, { 3., 4. } } } }; constexpr Bases b = { { 0, 'c', 1.f, 1. }, { { 1 }, { 'a', 'b' }, { 1.f, 2.f, 3.f }, { { 1., 2. }, { 3., 4. } } } }; static_assert(a == b); static_assert(!(a != b)); static_assert(!(a < b)); static_assert(a <= b); static_assert(!(a > b)); static_assert(a >= b); } The program ultimately ICEs gcc10 but working with a reduced repro shows some other gaps: struct Arrays { int a[2]; #ifdef MEMBERS auto operator<=>(const Arrays&) const = default; #endif #ifdef FRIENDS friend auto operator<=>(const Arrays&, const Arrays&) = default; // friend bool operator==(const Arrays&, const Arrays&) = default; // should be implicitly declared #endif }; int main() { constexpr Arrays a1 { 1, 2 }; constexpr Arrays a2 { 3, 4 }; static_assert(a1 == a1); // OK static_assert(a1 != a2); // OK static_assert(a1 < a2); // ICE } When MEMBERS is defined it only ICEs at the final static assert, but with FRIENDS it both leaves the implicitly declared operator== undeclared _and_ ICEs. Additionally, replacing `auto` with `std::strong_ordering` produces an ICE in finish_expr_stmt so I assume arrays just aren't handled yet?
Confirmed: 92426.C: In member function ‘constexpr auto Basics::operator<=>(const Basics&) const’: 92426.C:6:8: internal compiler error: tree check: expected class ‘type’, have ‘exceptional’ (error_mark) in is_cat, at cp/method.c:999 6 | auto operator<=>(const Basics&) const = default; | ^~~~~~~~ 0x18bbf02 tree_class_check_failed(tree_node const*, tree_code_class, char const*, int, char const*) /home/mpolacek/src/gcc/gcc/tree.c:9726 0x87f90b tree_class_check(tree_node*, tree_code_class, char const*, int, char const*) /home/mpolacek/src/gcc/gcc/tree.h:3395 0xa33a2e is_cat /home/mpolacek/src/gcc/gcc/cp/method.c:999 0xa33bc7 cat_tag_for /home/mpolacek/src/gcc/gcc/cp/method.c:1011 0xa34a09 common_comparison_type /home/mpolacek/src/gcc/gcc/cp/method.c:1150 0xa3560b build_comparison_op /home/mpolacek/src/gcc/gcc/cp/method.c:1325 0xa3669c synthesize_method(tree_node*) /home/mpolacek/src/gcc/gcc/cp/method.c:1485 0x9b7744 mark_used(tree_node*, int) /home/mpolacek/src/gcc/gcc/cp/decl2.c:5485 0x8a02ec build_over_call /home/mpolacek/src/gcc/gcc/cp/call.c:8946 0x8952f2 build_new_op_1 /home/mpolacek/src/gcc/gcc/cp/call.c:6224 0x895f2a build_new_op(op_location_t const&, tree_code, int, tree_node*, tree_node*, tree_node*, tree_node**, int) /home/mpolacek/src/gcc/gcc/cp/call.c:6490 0xa3555c build_comparison_op /home/mpolacek/src/gcc/gcc/cp/method.c:1319 0xa3669c synthesize_method(tree_node*) /home/mpolacek/src/gcc/gcc/cp/method.c:1485 0x9b7744 mark_used(tree_node*, int) /home/mpolacek/src/gcc/gcc/cp/decl2.c:5485 0x8a02ec build_over_call /home/mpolacek/src/gcc/gcc/cp/call.c:8946 0x8952f2 build_new_op_1 /home/mpolacek/src/gcc/gcc/cp/call.c:6224 0x895f2a build_new_op(op_location_t const&, tree_code, int, tree_node*, tree_node*, tree_node*, tree_node**, int) /home/mpolacek/src/gcc/gcc/cp/call.c:6490 0xbde344 build_x_binary_op(op_location_t const&, tree_code, tree_node*, tree_code, tree_node*, tree_code, tree_node**, int) /home/mpolacek/src/gcc/gcc/cp/typeck.c:4222 0xa789a3 cp_parser_binary_expression /home/mpolacek/src/gcc/gcc/cp/parser.c:9645 0xa78e02 cp_parser_assignment_expression /home/mpolacek/src/gcc/gcc/cp/parser.c:9780 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.
Please note that the submitted test program seems not to meet the #include requirement as articulated in N4835 clause [expr.spaceship] p10: "10 The five comparison category types (17.11.2) (the types std::strong_ordering, std::strong_equality, std::weak_ordering, std::weak_equality, and std::partial_ordering) are not predefined; if the header <compare> (17.11.1) is not included prior to a use of such a class type – even an implicit use in which the type is not named (e.g., via the auto specifier (9.2.8.5) in a defaulted three-way comparison (11.11.3) or use of the built-in operator) – the program is ill-formed."
(In reply to W E Brown from comment #2) > Please note that the submitted test program seems not to meet the #include > requirement as articulated in N4835 clause [expr.spaceship] p10: > > "10 The five comparison category types (17.11.2) (the types > std::strong_ordering, std::strong_equality, std::weak_ordering, > std::weak_equality, and std::partial_ordering) are not predefined; if the > header <compare> (17.11.1) is not included prior to a use of such a class > type – even an implicit use in which the type is not named (e.g., via the > auto specifier (9.2.8.5) in a defaulted three-way comparison (11.11.3) or > use of the built-in operator) – the program is ill-formed." My mistake, I over simplified the example. There should have been a #include <compare> in both cases.
I can't reproduce the ICE in GCC 10.1.0 or 11.1.0 or on the trunk.