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From: "nunoplopes at sapo dot pt" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/98842] New: optional's spaceship operations generates
 wrong code when operator== is not present
Date: Tue, 26 Jan 2021 18:09:59 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98842

            Bug ID: 98842
           Summary: optional's spaceship operations generates wrong code
                    when operator=3D=3D is not present
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nunoplopes at sapo dot pt
  Target Milestone: ---

struct expr {
  std::strong_ordering operator<=3D>(const expr &rhs) const;
  //bool operator=3D=3D(const expr &rhs) const;
};

int f() {
  return std::is_eq(std::optional<expr>() <=3D> std::optional<expr>());
  //return std::optional<expr>() =3D=3D std::optional<expr>();
}


Function f() is compiled to 0 like that. But if you uncomment the
expr::operator=3D=3D line, it returns 1.

https://gcc.godbolt.org/z/fv85eP=