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Hole-y partial type signatures greatly slow down compile times

This time, I actually mean it. :)

Originally reported here, I distilled the example from this comment into a one file test case. Sigs.hs is exactly like NoSigs.hs, except for the fact that it has a bunch of extra type signatures that have a lot of holes. On my machine, this is what compilation times are (I gave up timing after 15 minutes):

GHC version 8.0.2 8.2.1 8.4.1 (445554b6)
`NoSigs.hs` 24.13s 22.93s 34.05s
`Sigs.hs` \>15m \~13m \>15m
Edited by Alec Theriault
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