bpo-46471: use global singletons for single byte bytes objects

[kumaraditya303]

By using global singletons for single byte bytes objects in deepfreeze, there is no need to generate c code for it so it reduces the size of generated c file and reduces memory use of the objects when they are allocated on the heap as now they are statically allocated and they are already immortal.

https://bugs.python.org/issue46471

[gvanrossum]

How many of these do you see in deepfreeze.c? Singletons byte literals aren’t that common I guess.

[kumaraditya303]

How many of these do you see in deepfreeze.c? Singletons byte literals aren’t that common I guess.

❯ cat Python/deepfreeze/deepfreeze.c | grep "(PyObject \*)&_Py_SINGLETON(bytes_characters" | wc -l
200

[gvanrossum]

Ah, I see. co_localspluskinds is a bytes object (flags for args and local vars) and when there's exactly one of those, it qualifies. Clever.