[Bug c++/107065] New: GCC treats rvalue like lvalue

["jlame646 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107065

            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 = "prvalue";
};

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

template<typename T>
struct value_category<T&&> {
    static constexpr auto value = "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 = true;

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

```