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I tried to compile one of our server applications with 8.2.1 (which compiles fine with 8.0.2).

The compilation runs smoothly, but when it reaches a specific file, the RAM usage goes up to > 20GB pretty fast on my 16GB machine and the GHC process gets terminated with a stack overflow error.

I tried to find a minimal example that causes this behavior:

#!/usr/bin/env stack
-- stack --resolver nightly-2017-08-25 script

{-# LANGUAGE ApplicativeDo #-}

x = do
    (a, _) <- undefined
    (b, _) <- undefined
    (c, _) <- undefined
    undefined

main = undefined

It only happens with at least 3 of these pattern matches.