long compile time question

[Maxim Fomin]

On Wednesday, 24 October 2012 at 09:50:38 UTC, Era Scarecrow 
wrote:
> On Wednesday, 24 October 2012 at 04:49:19 UTC, 1100110 wrote:
>>> The following takes nearly three minutes to compile.
>>> The culprit is the line bar ~= B();
>>> What is wrong with this?
>
>> I have the same issue on linux x64 2.060
>>
>> So appending to a dynamic array isn't really that efficient. 
>> But this goes WAY over that line.  I'm timing your test now.
>>
>> It's still going...
>
>  It appears it's all happening during copying init, why I am 
> not sure.
>
> [code]
> struct B {
>   enum SIZE = 1024 * 64;
>   int[SIZE] x;
> }
>
> //same timing issue, no array involved
> void test(B b) {}
>
> void main() {
>   test(B());
> }
> [/code]
>
>  I've changed the *64 to various numbers and gotten curious 
> results. The mb is the noted (estimated) memory footprint it 
> used during compiling.
>
> 1:   0m0.725s   mb:??
> 2:   0m1.414s   mb:??
> 4:   0m2.620s   mb:28
> 8:   0m8.937s   mb:30
> 16:  0m35.869s  mb:34
> 32:  2m36.922s  mb:42
> 64:  9m27.353s  mb:56

According to assembly dmd just generates repetitive instructions 
to zero memory instead of making it in a loop. A workaround is to 
initialize array to void and then zero it in a loop.