[GSoC] 'Independency of D from the C Standard Library' progress and update thread

[Piotrek]

On Saturday, 6 July 2019 at 11:07:41 UTC, Stefanos Baziotis wrote:
>> As for the benchmarks.
>> I think you can post your results somewhere. Or you did. 
>> Unfortunately I cannot find them.
>
> You're right, my mistake, there are no recent benchmarks. I'll 
> try to post
> today. They're similar to yours.


>> I tested Dmemset with dmd (lcd and gdc didn't compile) on 
>> i3-3220 at 3.30GHz (Ubuntu).
>
> That's weird. Could you give some more info on how did you 
> compile?

I used the old repo for Dmemset. With Dmemutils it works now. I 
removed static foreach from benchmark.d in order to run gdc.
Text results:
https://github.com/PiotrekDlang/Dmemutils/tree/master/Dmemset/output

>
>> The strange thing is I get different results when I change the 
>> following line in benchamrks.d
>> So D version becomes better. Maybe this is related to 
>> different binary file after compilation.
>
> That is indeed strange but not too unexpected. A compiler (more 
> possible in
> the DMD back-end) might decide to do strange things for reasons 
> I don't know.
> I'll try to re-create similar behavior in mine.

It seems it wasn't related to this change. Looks like heisen 
optimization.

>
> Just some more info for anyone interested:
> Regarding sizes 1-16. With GDC / LDC, in my benchmarks
> (and by reading the ASM, I assume in all the benchmarks), it 
> reaches parity
> with libc (note that for sizes 1-16 the naive version is used,
> meaning, a simple for loop). Now, for such small sizes, the 
> standard way to go
> is a fall-through switch (I can give more info on that if 
> someone is interested).
> The problem with that is that it's difficult to be optimized 
> along with the rest
> of the code. Meaning, by the compiler. Or at least, I didn't 
> find a way
> to do it. And so, I use the naive version which is only 
> slightly slower but
> doesn't affect bigger sizes.

Funnily enough, DMD (with Dmemset) holds the speed record, over 
50 GB/s, copying some big block sizes.
However, aren't smaller sizes more important?


> My guess is that especially with GDC / LDC (and DMD, but I'm 
> not yet sure
> for DMD across different hardware), Dmemset can actually 
> replace libc memset().

One issue is it should be tested on all variation of HW and OS.
At least it can be placed in experimental module.


Cheers,
Piotrek