mypyc: Fix overflow in id function (CPyTagged_Id)

[onlined]

Description

In CPython, the id of an object is its address. It's computed by converting the pointer to an unsigned integer (PyLong_FromVoidPtr). A similar logic is present here, pointer is converted to a Py_ssize_t and CPyTagged_FromSsize_t is called with that integer.

There is a problem with that approach: Py_ssize_t cannot hold every pointer value. Sometimes overflow happens and CPyTagged_FromSsize_t is called with a negative integer.

With the new approach, the number is checked: If it fits in a Py_ssize_t, CPyTagged_FromSsize_t is called. If not, it is directly
converted to a PyObject using PyLong_FromVoidPtr.

Fixes #11148.

Test Plan

I used the Docker test in #11148. I could reproduce failure before the changes, it passed after the changes.

[jhance]

Random question - is the size only insufficient on the platforms where the bug was found? I'm wondering if we can skip the check on x8664 although maybe complicating things isn't worth that micro optimization.

[onlined]

From this answer, it seems like on Linux x86_64 and Linux arm64, the user space addresses (57 bit long maximum) don't reach PY_SSIZE_T_MAX (63 bit long on these platforms), so the bug doesn't cause any trouble. But on different processor architectures and kernels, this might change. I am not sure about going for that optimization, I think it's not worth relying on an implementation detail (if this is guaranteed, my opinion could change) for eliminating a function call and an integer comparison.

[mr-c]

Thanks!