floatExpr tick break<2>

When running the Shake test suite against GHC HEAD I get:

ghc: panic! (the 'impossible' happened)
  (GHC version 7.11.20150615 for x86_64-unknown-linux):
	floatExpr tick break<2>()

Full log at https://travis-ci.org/ndmitchell/shake/jobs/67636563. The command line that produced it is:

runhaskell -ignore-package=hashmap -ioutput/docs/ -isrc output/docs/Main.hs

If this seems like a legitimate bug that you don't already know about and are interested in tracking down, I'll try and grab the output/docs directory (it's on a remote machine I don't have access to on a different OS with a compiler I don't have installed, so it's not trivial to find it, but should be possible).

Trac metadata

Trac field	Value
Version	7.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	ndmitchell@gmail.com
Operating system
Architecture