[expr.reinterpret.cast] p2 says

An expression of integral, enumeration, pointer, or pointer-to-member type can be explicitly converted to its own type; such a cast yields the value of its operand.

What does "its own type" mean? Does it mean the identical original type or something else? Consider this example:

reinterpret_cast<int>(10);
reinterpret_cast<int const>(10);
reinterpret_cast<int volatile>(10);
reinterpret_cast<int const volatile>(10);

Both GCC and Clang accept this example. I think such a conversion is intended to be regulated by [expr.reinterpret.cast] p2. Because p1 says

Conversions that can be performed explicitly using reinterpret_­cast are listed below. No other conversion can be performed explicitly using reinterpret_­cast.

Except that p2 might be relevant to this example, all other rules are irrelevant to the above example. It is necessary to clarify what "its own type" means. Presumably, it means

An expression of integral, enumeration, pointer, or pointer-to-member type can be explicitly converted to the cv-unqualified version or cv-qualification of that type.