[Issue 18843] -deps -unittest causes cataclysmic memory usage

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18843

--- Comment #2 from FeepingCreature <default_357-line at yahoo.de> ---
Note: This has gotten a lot better at some point, great job! But running with
`-deps` still brings the time for a simple Hello World up from 250ms wallclock
to 440ms wallclock. It is thus still unusable, as its whole point would be
speeding up compiles, and as it stands I can get the import graph of projects a
lot faster by just grepping for `import`.

--