Compiler nontermination on UNPACK pragmas

Feeding GHC 7.6.1 (from git) ill-advised UNPACK pragmas like

data T1 = T1 {-# UNPACK #-} !T1

results in GHC going into infinite wait; gdb reports

#1  0x0000000001f7f979 in waitCondition ()
#2  0x0000000001f68c3b in yieldCapability ()
#3  0x0000000001f712d2 in schedule ()
#4  0x0000000001f727b5 in scheduleWaitThread ()
#5  0x0000000001f6f40e in real_main ()
#6  0x0000000001f6f50a in hs_main ()
#7  0x0000000000495763 in main ()

This happens, apparently, whenever there's possible recursion through an UNPACK pragma, even in the (I think) well-formed

data T0 = T0 T1
data T1 = T1 {-# UNPACK #-} !T0

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture