[Python-Dev] Re: Prospective Peephole Transformation

[Phillip J. Eby]

At 04:45 PM 2/18/05 +0100, Fredrik Lundh wrote:
>Phillip J. Eby wrote:
>
> >>Only contains expressions are translated:
> >>
> >>     "if x in [1,2,3]"
> >>
> >>currently turns into:
> >>
> >>     "if x in (1,2,3)"
> >>
> >>and I'm proposing that it go one step further:
> >>
> >>     "if x in Seachset([1,2,3])"
> >
> > ISTM that whenever I use a constant in-list like that, it's almost 
> always with just a few (<4)
> > items, so it doesn't seem worth the extra effort (especially disrupting 
> the marshal module) just
> > to squeeze out those extra two comparisons and replace them with a 
> hashing operation.
>
>it could be worth expanding them to
>
>     "if x == 1 or x == 2 or x == 3:"
>
>though...
>
>C:\>timeit -s "a = 1" "if a in (1, 2, 3): pass"
>10000000 loops, best of 3: 0.11 usec per loop
>C:\>timeit -s "a = 1" "if a == 1 or a == 2 or a == 3: pass"
>10000000 loops, best of 3: 0.0691 usec per loop
>
>C:\>timeit -s "a = 2" "if a == 1 or a == 2 or a == 3: pass"
>10000000 loops, best of 3: 0.123 usec per loop
>C:\>timeit -s "a = 2" "if a in (1, 2, 3): pass"
>10000000 loops, best of 3: 0.143 usec per loop
>
>C:\>timeit -s "a = 3" "if a == 1 or a == 2 or a == 3: pass"
>10000000 loops, best of 3: 0.187 usec per loop
>C:\>timeit -s "a = 3" "if a in (1, 2, 3): pass"
>1000000 loops, best of 3: 0.197 usec per loop
>
>C:\>timeit -s "a = 4" "if a in (1, 2, 3): pass"
>1000000 loops, best of 3: 0.225 usec per loop
>C:\>timeit -s "a = 4" "if a == 1 or a == 2 or a == 3: pass"
>10000000 loops, best of 3: 0.161 usec per loop
>
></F>

Were these timings done with the code that turns (1,2,3) into a constant?

Also, I presume that these timings still include extra LOAD_FAST operations 
that could be replaced with DUP_TOP in the actual expansion, although I 
don't know how much difference that would make in practice, since saving 
the argument fetch might be offset by the need to swap and pop at the end.