Bug report

Bug description:

The pickletools.optimize code suddenly performs bad starting with python 3.14, with or without JIT.
The degradation is a factor 3 to 4.

It is easy to test.

First use this script to make a sizeable dict and pickle it and write it to file.

import pickle

x = {}

for i in range(1, 1000000):
    x[i] = f"ii{i:>07}"

with open("pickled", "wb") as fh:
    pickle.dump(x, fh, protocol=4)

Then write a script, let's call it optpickle.py to read the pickled dict from file and optimize it and write the result to another file.

# optpickle.py

import pickletools

with open("pickled", "rb") as fh:
    p = fh.read()

s = pickletools.optimize(p)

with open("pickledopt", "wb") as fh:
    fh.write(s)

Now execute this in three separate terminal windows, one geared to python 3.13, one to python 3.14.0 without JIT, and one to python 3.14.0 with JIT.

My results on a mac with M1 processor were

That is a dramatic drop in performance!

The filesizes are 16.9 MB for the unoptimized file and 15.9 for the optimized one.

I decided to drop the optimization in an app where I used it heavily

CPython versions tested on:

3.14

Operating systems tested on:

macOS