RetroSearch Browse

Fri Mar 11 01:41:12 CET 2011 · https://mail.python.org/pipermail/python-dev/2011-March/109080.html

Well, that was just a though. You're right that long runs of constants
can appear, and it's better to avoid pathological behaviour in such
cases.
Your second path looks good.

Eugene

On Thu, Mar 10, 2011 at 6:30 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> On Thu, 10 Mar 2011 02:17:34 +0000 (UTC)
> Eugene Toder <eltoder at gmail.com> wrote:
>> > Indeed, see http://bugs.python.org/issue11244
>>
>> Yes, I've noticed that too. However, if I'm not missing something, your patches
>> do not address folding of -0.
>>
>> Btw, there's an alternative approach to allow "recursive" constant folding.
>> Instead of keeping a stack of last constants, you can keep a pointer to the
>> start of the last (LOAD_CONSTs + NOPs) run and the number of LOAD_CONSTs in
>> that run (called lastlc in the current version). When you want Nth constant
>> from the end, you start from that pointer and skip lastlc-N constants. You
>> also make a function to get next constant from that point. This approach has
>> worse time complexity for searching in a long run of LOAD_CONSTs,
>
> Yes, the stack basically acts as a cache to avoid computing all this
> again and again.
>
>> however,
>> there are upsides:
>> - very long runs of constants are rare in real code
>
> True, but they might appear in generated code.
>
>> - it uses less memory and doesn't have arbitrary limits on the size of the run
>
> Neither does the latest patch.
>
>> - it's book-keeping overhead is smaller, so when you don't have long runs of
>> constants (common case, I believe), it should be faster
>
> The book-keeping overhead should be quite small really, it's a simple
> autogrowing array with O(1) access and amortized append time. What's
> left is the overhead of the initial malloc() (and final free()).
>
>> - I think it's simpler to implement
>
> Feel free to propose an alternate patch, but I'm not sure that it would
> be significantly simpler (and a stack is a well-known data structure).
> Also, please present some benchmarks if you do.
>
> Regards
>
> Antoine.

Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://mail.python.org/pipermail/python-dev/2011-March/109080.html below:

[Python-Dev] constant folding of -0