Using D

[simendsjo via Digitalmars-d]

On 07/11/2014 06:28 PM, Russel Winder via Digitalmars-d wrote:
> On Fri, 2014-07-11 at 17:43 +0200, simendsjo via Digitalmars-d wrote:
> […]
>> A little anecdote.. I once got a 20% speed increase in Python by
>> "moving" a variable instantiation outside a tight loop.
>>   i = 0
>>   # loop here
>>     i = something
>>
>> rather than
>>   # loop here
>>     i = something
> 
> This is interesting. I can believe there is some performance benefit,
> but I am not sure I believe 20% improvement. If you can send me the code
> you were using, I would like to do some benchmarking on this.

Yes, I was very perplexed when I was profiling and finally found the
main offender. Unfortunately I don't have the code - it was a project
done for a past employer back in 2006/2007 (Python 2.4 IIRC).

>> The compiler wasn't smart enough to do this.
> 
> The Python compiler cannot and will never be able to do any such thing.
> Indeed if it did any such thing, it would be an error since it
> significantly changes the semantics of the program. Thus not doing this
> is not the fault of the compiler.  The fact that you were able to do
> this and it appeared to give you the same results just means that the
> change in program semantics did not affect your computation. Which is
> good, but not something the compiler could determine.

I think of this as a fault in the compiler. It was quite obvious (to me)
that nothing else relied on the value so the value didn't have to be
created on each iteration.