[fpc-devel] First pas2js public release

[Benito van der Zander]

Hi,

> Of course not. First of all 100000 is ridiculously small and second
> the above example is probably optimized by the engine.
> For example under V8 with 100000000 iterations you get 1.1s and 1.9s.

It is not so small or optimized with Firefox.

It took around 100ms

With 10000000, it gives 5479ms and 4814ms, i.e. the array is faster here

With 100000000 the script does not complete, before Firefox ask "do you 
want to stop the too slow script"

> Like what?
> What pointer code do you want to port?
>

I have not looked at any specific.

But recently I have started to change everything to pointers.

For example when you have an array and want a subrange without the first 
element of the array, you can either copy almost everything in a new 
array, or just use a pointer to the second element.

Or in my XQuery interpreter I used interfaces to get ref counting, but 
at many places the ref counting was too slow, so I replaced it with 
pointers to interfaces.

E.g. when iterating over an array of interfaces with an enumerator. for 
x in thearray do, the array keeps the ref count >= 1, so x is much more 
efficient as pointer to an interface.



> Isn't that a contradiction to "port all existing"?

Not with full program static analysis

Or people could mark the values they need as pointers in other units (by 
adding an unused public function just accessing it as pointer)

Best,
Benito



On 18.12.2017 17:19, Mattias Gaertner wrote:
> On Mon, 18 Dec 2017 14:55:53 +0100
> Benito van der Zander<benito at benibela.de>  wrote:
>
>> [...]
>>> That would be quite a slow down.
>> Is it?
>>
>> I saw no speed difference between
>>
>> var x = 1;
>> for (var i=0;i<100000;i++) x++;
>>
>> and
>>
>> var x = [1];
>> for (var i=0;i<100000;i++) x[0]++;
>>
>> in Firefox.
> Of course not. First of all 100000 is ridiculously small and second
> the above example is probably optimized by the engine.
> For example under V8 with 100000000 iterations you get 1.1s and 1.9s.
>
> Test with some more real world code.
>
>> Perhaps more memory usage
> Pretty sure more memory usage.
>
>   
>>> Isn't speed the main idea of using pointers?
>> It would be to port all existing pascal code
> Like what?
> What pointer code do you want to port?
>
>
>>> Also what if var and @var are in different units?
>> Either it needs full program static analysis, or pointers are only
>> allowed to something that was used with a pointer in its unit
> Isn't that a contradiction to "port all existing"?
>
>
>>> You may want to take a look at asm.js, which has a working
>>> model for emulating pointers in JavaScript. It would be possible to add
>>> a pas2js target for that. But then again there is webassembly
>>> as well and it seems to have better support.
>> That model looks like quite a slow down
> The js engines have some optimizations for that model.
>
> Mattias
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