Data.Vector.foldl' hangs GHC indefinitely with -O2

Running 'ghc -O2 -fforce-recomp -c Bug.hs' on the following

module Bug where

import qualified Data.Vector as V

data Tree = Empty | Node !(V.Vector Tree)

f :: k -> Tree -> Tree
f k' (Node ch) = head $ V.foldl' (\u t' -> case t' of Empty -> u; _ -> t' : u) [] ch

will hang forever (or at least >5m). Builds fine with -O1 / V.foldl.

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Compiler
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