Performance regression in nightly

[valff]

nightly-2018-11-26 introduced 10x compile time slow-down compared to nightly-2018-11-25. Here is a minimal working example: https://github.com/valff/rustc-perf-regression

[nikic]

Perf top has the majority of the time spent in _ZN5rustc5infer9InferCtxt20create_next_universe17hea623e9d2897e73eE, so this is very likely due to #55921, which is already being fixed at #56251.

[valff]

That's great. I will test with the next nightly tomorrow and close the issue if it's fixed.

[valff]

I confirm that version 400c2bc5e 2018-11-27 fixes this. It is even 5% better than before! Very nice, thank you.