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From: "jlame646 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107065] New: GCC treats rvalue like lvalue
Date: Wed, 28 Sep 2022 07:35:09 +0000
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X-Bugzilla-Version: 12.2.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107065

            Bug ID: 107065
           Summary: GCC treats rvalue like lvalue
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jlame646 at gmail dot com
  Target Milestone: ---

In the following program gcc incorrectly treats the expression `!(!b)` as
lvalue. Demo: https://godbolt.org/z/zv5En5hjG

```
#include <iostream>
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

int main() {
    bool b =3D true;

    std::cout << VALUE_CATEGORY(!(!b)); //gcc wrongly prints lvalue
}

```=