A Friendly Challenge for D

[welkam]

So I run profiler and 97% of time is spent in void twinsSieve 
function and hotspots are seg[k] = seg[k] |  1; lines. Since 
seg[k] can only be 1 or 0 I removed that or operation. And the 
results are. Queue the drum-roll... 5% slower.

I thought that all of my studying was getting somewhere. That I 
beginning to understand things but no. Performing OR operation 
and then storing data is faster than just storing data. [sarcasm] 
Of course it makes sense [/sarcasm]

I looked at assembler and nothing changed except

orb    $0x1,(%rbx,%rdi,1)

is changed to

movb   $0x1,(%rbx,%rdi,1)

I`m completely lost.