[Bug c++/95567] New: Defaulted virtual <=> has the wrong behavior

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95567

            Bug ID: 95567
           Summary: Defaulted virtual <=> has the wrong behavior
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: barry.revzin at gmail dot com
  Target Milestone: ---

Reduced from Twitter user @feder_and_ink:

#include <compare>

struct B {
  B(int i) : i(i) {}

  VIRTUAL std::strong_ordering operator<=>(B const& other) const = default;
  int i;
};

struct D : B {
  D(int i, int j) : B(i), j(j) {}
  int j;
};

bool check() {
    return B(2) == D(2, 3);
}

With -DVIRTUAL=, check() returns true.
With -DVIRTUAL=virtual, check() erroneously returns false.
On compiler explorer: https://godbolt.org/z/hc3U5f