DMD compilation speed

[Andrew Godfrey via Digitalmars-d]

I just upgraded from DMD 2.065.0 (so about 2 years old) to 
2.070.0, and noticed a difference in compilation speed. I'll 
detail what I see, in case it's interesting, but really I just 
want to ask: What should I expect? I know that DMD is now 
selfhosting, and I know there's a tradeoff between compilation 
speed and speed of generated code. Or maybe it's just a tweak to 
default compiler options.
So maybe this is completely known.

What I see:
DMD 32 running on Windows 10, on my laptop that's quite a few 
years old.
Random tiny single-file .d program; I'm looking at what happens 
when I make a change and then run the program (with or without 
"-unittest").

On 2.065.0: This takes around 1.9 seconds. On 2.070.0: This takes 
around 3.6 seconds.

I really don't want to trigger an investigation if this is just 
an anomaly - I'm still quite happy with 4 seconds to compile and 
run unit tests. I mainly mention it in case it's an interesting 
surprise.