[GHC] #8900: Strictness analysis regression

[GHC]

#8900: Strictness analysis regression
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        Reporter:  tibbe                    |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:
       Component:  Compiler                 |          Version:  7.8.1-rc2
      Resolution:                           |         Keywords:
Operating System:  MacOS X                  |     Architecture:  x86_64
 Type of failure:  Runtime performance bug  |  (amd64)
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"0b6fa3e95078797f87302780a85607decab806fb/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="0b6fa3e95078797f87302780a85607decab806fb"
 Eliminate redundant seq's (Trac #8900)

 This patch makes the simplifier eliminate a redundant seq like
     case x of y -> ...y....
 where y is used strictly.  GHC used to do this, but I made it less
 aggressive in

    commit 28d9a03253e8fd613667526a170b684f2017d299 (Jan 2013)

 However #8900 shows that doing so sometimes loses good
 transformations; and the transformation is valid according to "A
 semantics for imprecise exceptions".  So I'm restoring the old
 behaviour.

 See Note [Eliminating redundant seqs]
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8900#comment:18>
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