GHC 8.8 heap overflow regression
The following program throws a heap overflow if you compile it with optimization on GHC 8.8 and HEAD:
```haskell
module Bug where
import Data.Bits (setBit)
f :: Int
f = foldl setter 0 $ zip [0..] [()]
where
setter v (ix, _) = setBit v ix
```
```
$ ~/Software/ghc3/inplace/bin/ghc-stage2 -fforce-recomp -O Bug.hs
[1 of 1] Compiling Bug ( Bug.hs, Bug.o )
ghc-stage2: panic! (the 'impossible' happened)
(GHC version 8.9.20190309 for x86_64-unknown-linux):
heap overflow
```
This does not happen with GHC 8.6.4.
The `FontyFruity` package on Hackage fails to build on GHC HEAD due to this regression.
issue