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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107065] GCC treats rvalue as an lvalue
Date: Wed, 28 Sep 2022 12:00:25 +0000
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X-Bugzilla-Component: c++
X-Bugzilla-Version: 12.2.0
X-Bugzilla-Keywords: wrong-code
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107065

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-09-28

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced to remove the library dependency:

enum Cat { prvalue, lvalue, xvalue };

template<typename T>
struct value_category {
    // Or can be an integral or enum value
    static constexpr auto value =3D prvalue;
};

template<typename T>
struct value_category<T&> {
    static constexpr auto value =3D lvalue;
};

template<typename T>
struct value_category<T&&> {
    static constexpr auto value =3D xvalue;
};

// Double parens for ensuring we inspect an expression,
// not an entity
#define VALUE_CATEGORY(expr) value_category<decltype((expr))>::value

constexpr bool global =3D true;
static_assert( VALUE_CATEGORY(!(!global)) =3D=3D prvalue, "GCC gets this ri=
ght" );

int main()
{
  bool b =3D true;
  if ( VALUE_CATEGORY(!(!b)) !=3D prvalue )
    throw 1;
}=