Message 352782 - Python tracker

I prefer to keep it a macro. The compiler does not know that it is never executed, so it can generate a suboptimal code.

While it is a macro, it can be made a no-op, or even with compiler-specific instructions like __builtin_unreachable. This can help the compiler to generate more optimal code. For example, the popular idiom:

    switch (kind) {
    case PyUnicode_1BYTE_KIND: {
        ...
        break;
    }
    case PyUnicode_2BYTE_KIND: {
        ...
        break;
    }
    case PyUnicode_4BYTE_KIND: {
        ...
        break;
    }
    default: Py_UNREACHABLE();
    }

could be compiled to the code equivalent to:

    if (kind == PyUnicode_1BYTE_KIND) {
        ...
        break;
    }
    else if (kind == PyUnicode_2BYTE_KIND) {
        ...
        break;
    }
    else { // assuming (kind == PyUnicode_4BYTE_KIND)
        ...
        break;
    }