[GHC] #8091: retry# lacks strictness information

[GHC]

#8091: retry# lacks strictness information
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        Reporter:  parcs             |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.3
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 #13916 leads me to believe this is strictness signature is too strong.
 Consider this program,
 {{{#!hs
 loop :: [TMVar a] -> STM a -> STM a
 loop []     m = m
 loop (x:xs) m = loop xs (m `orElse` takeTMVar x)

 doIt :: [TMVar Int] -> STM Int
 doIt xs = atomically $ loop xs retry
 }}}

 GHC will currently give `loop` a strictness signature of
 `<S,1*U><C(S),1*C1(U(U,U))>`. So this means that if we give `retry#` a
 divergent result demand GHC incorrectly assume that `loop xs retry` will
 itself diverge, which is clearly not true.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8091#comment:7>
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