gh-126703: add freelist for ints with small number of digits

[eendebakpt]

Benchmark:

bench_gcd: Mean +- std dev: [main] 194 us +- 5 us -> [pr2] 184 us +- 6 us: 1.05x faster
bench_uuid8: Mean +- std dev: [main] 1.69 us +- 0.04 us -> [pr2] 1.64 us +- 0.02 us: 1.03x faster
bench_id: Mean +- std dev: [main] 48.2 us +- 1.4 us -> [pr2] 41.6 us +- 1.0 us: 1.16x faster

Benchmark hidden because not significant (1): bench_int

Geometric mean: 1.06x faster

The bench_int is not affected since the compact ints already have a freelist in current main. The bench_id is a microbenchmark that does minimal amount of work. The bench_gcd and bench_uuid8 are benchmarks that are representative for real code.

Statistics for the number of allocations saved can be found in the corresponding issue.

Benchmark script:

# Quick benchmark for cpython freelists for int

from uuid import uuid8
import pyperf


def collatz(a):
    while a > 1:
        if a % 2 == 0:
            a = a // 2
        else:
            a = 3 * a + 1

def bench_int(loops):
    range_it = range(loops)
    tpl = tuple(range(200, 300))

    t0 = pyperf.perf_counter()
    for ii in range_it:
        for jj in tpl:
            collatz(jj)
    return pyperf.perf_counter() - t0

def gcd(x, y):
    while y != 0:
        (x, y) = (y, x % y)
    return x

def bench_gcd(loops):
    range_it = range(loops)
    tpl = tuple(range(100))

    t0 = pyperf.perf_counter()
    for ii in range_it:
        for a in tpl:
            gcd( (2<<120) + 1231231232131, 2<<30+ a)
    return pyperf.perf_counter() - t0

def bench_uuid8(loops):
    range_it = iter(range(loops))

    t0 = pyperf.perf_counter()
    for ii in range_it:
        _ = uuid8()
    return pyperf.perf_counter() - t0

def bench_id(loops):
    range_it = iter(range(loops))

    t0 = pyperf.perf_counter()
    for ii in range_it:
        for jj in range(1000):
            _ = id(jj)
    return pyperf.perf_counter() - t0


if __name__ == "__main__":
    runner = pyperf.Runner()
    runner.bench_time_func("bench_int", bench_int)
    runner.bench_time_func("bench_gcd", bench_gcd)
    runner.bench_time_func("bench_uuid8", bench_uuid8)
    runner.bench_time_func("bench_id", bench_id)

• Issue: Use freelist for range object, iterator objects and other often used objects #126703

[efimov-mikhail]

Why ints[1] is used here?
Maybe some comment on it will be useful?

[skirpichev]

Here we need only ndigits==1 integers.

New implementation uses several free lists (though, ints[0] isn't used).

[eendebakpt]

ints[0] is indeed not used. It takes a tiny bit of extra memory, but makes the code cleaner.

[efimov-mikhail]

Is it equivalent to run PyObject_Free(self) and to run Py_TYPE(self)->tp_free(self) for integers with PyLong_MAXSAVESIZE or more digits?

[eendebakpt]

It is for exact ints (but might not be for subclasses).

[efimov-mikhail]

LGTM, thanks for the answers.