Why is D's GC slower than GO's?

[rikki cattermole]

I have long argued that we should support it as an opt-in flag.

Because right now, if someone wants to experiment with these more 
powerful GC designs that can't. So there is no evidence that they 
couldn't benefit D.

At the very least it could generate some very interesting research 
papers if we find the right person to try it out. Especially for GC 
heavy applications like web services (vibe.d).