[GHC] #8091: retry# lacks strictness information

[GHC]

#8091: retry# lacks strictness information
-------------------------------------+------------------------------------
        Reporter:  parcs             |            Owner:
            Type:  bug               |           Status:  patch
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.3
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by parcs):

 To be clear, the form of dead code elimination that this change enables is

 replacing
 {{{
 #!haskell
 case retry# s1 of
     (# s2, a #) -> ...inaccessible..
 }}}

 with simply
 {{{
 #!haskell
 retry# s1
 }}}

 Such Core can appear after performing case-of-case on code like

 {{{
 #!haskell
 s <- readTVar v
 when (s > 0) retry
 ...
 }}}

 where everything after the `when` statement might get inlined under the
 scrutinization of `retry`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8091#comment:4>
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