System programming in D (Was: The God Language)

[Don]

On 29.12.2011 16:07, Vladimir Panteleev wrote:
> On Thursday, 29 December 2011 at 14:44:45 UTC, Don wrote:
>>> http://www.danielvik.com/2010/02/fast-memcpy-in-c.html . It doesn't even
>>> use inline assembler or compiler intrinsics.
>>
>> Note that the memcpy described there is _far_ from optimal. Memcpy is
>> all about cache effciency. DMD translates memcpy to the single
>> instruction "rep movsd" which you'd think would be optimal, but you
>> can actually beat it by a factor of four or more for long lengths.
>
> I've never seen DMD emit rep movsd. Does rep movsd even make sense when
> the memory areas do not have the same alignment? memcpy in snn.lib has a
> rep movsd instruction, but there's lots of other code (including what
> looks like Duff's device).

It's in the backend in cod2.c, line 3260. But on closer inspection -- 
you're right! It's in an
if(0 && ...) block.
So it never does it, even when everything's aligned.

There's a _huge_ potential for improvement in that function.