New submission from Batuhan Taskaya <isidenti...@gmail.com>:
Currently, all the slices are created by the interpreter with BUILD_SLICE preceded by 2/3 LOAD_CONSTS. We can move the slice creation into the compiler and deduce the cost of these 3/4 instructions into a single LOAD_CONST operation where all values in the slices are constants (like [:1], [::2], [-1]) which I assume the most common type. There are over 93.000 constant slices in 3.200~ PyPI packages, which I'd assume is a huge amount (ofc I don't claim to know that whether these are in loops / hot functions or static globals). Making these folding could save up to 1.32x on very common slicing behaviors (like <a list>[:1]). Here are the benchmarks (thanks to @pablogsal); *** -s "a=list(range(200))" "a[:1]" Mean +- std dev: [baseline] 61.8 ns +- 0.3 ns -> [optimized] 47.1 ns +- 0.2 ns: 1.31x faster (-24%) *** -s "a=list(range(200))" "a[1:1:1], a[::1], a[1::], a[1::1], a[::-1], a[-1::], a[:], a[::]" Mean +- std dev: [baseline] 2.38 us +- 0.02 us -> [optimized] 2.24 us +- 0.02 us: 1.06x faster (-6%) The macro benchmarks appeared to be +1.03x increase which is assumed as noise, so this is a targeted optimization. One problem with slices being constants is that, the code objects are hashable so does all the items in the co_consts tuple (also the internal dict that the compiler uses to store all co_const items). For allowing slices to be stored in the code objects, and not changing any behavior in a backward-incompatible way I'm proposing to make the slice objects hashable. It might not be seen as a feature, but a side-effect caused by this optimization. ---------- messages: 381759 nosy: BTaskaya, pablogsal priority: normal severity: normal status: open title: Move slice creation to the compiler for constants type: performance versions: Python 3.10 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue42454> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
