bpo-47009: Let PRECALL_NO_KW_LIST_APPEND do its own POP_TOP #32239

sweeneyde · 2022-04-01T18:37:02Z

Most code won't do y = L.append(x) or whatnot, so PRECALL_NO_KW_LIST_APPEND is almost always followed by POP_TOP. We can verify at specialization time.

This saves a Py_INCREF(Py_None), a SET_TOP(Py_None), and POP_TOP's Py_DECREF(POP()); DISPATCH();.

Some microbenchmarks:

from pyperf import Runner, perf_counter

def bench_append(loops, length):
    src = list(map(float, range(length)))
    arr = []
    t0 = perf_counter()

    for i in range(loops):
        arr.clear()
        for x in src:
            arr.append(x)

    return perf_counter() - t0

def bench_append_less_gc(loops, length):
    src = list(map(float, range(length)))
    out = [None] * loops
    t0 = perf_counter()

    for i in range(loops):
        arr = []
        for x in src:
            arr.append(x)
        out[i] = arr

    return perf_counter() - t0

runner = Runner()
for n in [100, 1_000, 10_000, 100_000]:
    runner.bench_time_func(f"append {n}", bench_append, n, inner_loops=n)
    runner.bench_time_func(f"append-less-gc {n}", bench_append_less_gc, n, inner_loops=n)

From GCC, --enable-optimizations, --with-lto:

- append 100000: 14.9 ns +- 0.3 ns -> 13.3 ns +- 0.4 ns: 1.12x faster
- append 10000: 15.1 ns +- 0.3 ns -> 13.6 ns +- 0.5 ns: 1.11x faster
- append-less-gc 100000: 16.4 ns +- 0.5 ns -> 14.9 ns +- 0.4 ns: 1.10x faster
- append 1000: 15.6 ns +- 0.3 ns -> 14.2 ns +- 0.3 ns: 1.09x faster
- append 100: 18.9 ns +- 0.6 ns -> 17.3 ns +- 0.6 ns: 1.09x faster
- append-less-gc 100: 27.4 ns +- 1.1 ns -> 25.2 ns +- 1.2 ns: 1.09x faster
- append-less-gc 10000: 19.2 ns +- 0.3 ns -> 17.8 ns +- 0.2 ns: 1.08x faster
- append-less-gc 1000: 22.0 ns +- 0.6 ns -> 20.8 ns +- 0.3 ns: 1.06x faster

Geometric mean: 1.09x faster

https://bugs.python.org/issue47009

Let PRECALL_NO_KW_LIST_APPEND do its own POP_TOP

344ee45

sweeneyde requested a review from markshannon as a code owner Apr 1, 2022

bedevere-bot added the awaiting core review label Apr 1, 2022

the-knights-who-say-ni added the CLA signed label Apr 1, 2022

sweeneyde added the skip news label Apr 1, 2022

Fix a copy/paste error

e0adb6a

sweeneyde force-pushed the listappend_pop branch from 43782cc to e0adb6a Compare Apr 1, 2022

Merge branch 'main' into listappend_pop

3361295

python / cpython Public

bpo-47009: Let PRECALL_NO_KW_LIST_APPEND do its own POP_TOP #32239

bpo-47009: Let PRECALL_NO_KW_LIST_APPEND do its own POP_TOP #32239

sweeneyde commented Apr 1, 2022 •

edited

python / cpython Public

bpo-47009: Let PRECALL_NO_KW_LIST_APPEND do its own POP_TOP #32239

Are you sure you want to change the base?

bpo-47009: Let PRECALL_NO_KW_LIST_APPEND do its own POP_TOP #32239

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sweeneyde commented Apr 1, 2022 • edited

sweeneyde commented Apr 1, 2022 •

edited