[GHC] #8569: ASSERT in testcase type-rep, only in some ways:

[GHC]

#8569: ASSERT in testcase type-rep, only in some ways:
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        Reporter:  nomeata           |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Test Suite        |          Version:  7.7
      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 nomeata):

 This might be related to Note [Don't optimise UProd(Used) to Used]. There
 it says

 > But with the joint demand of <Str, Used> doesn't convey any clue
 > that there is a product involved, and so the worthSplittingFun
 > will not fire.  (We'd need to use the type as well to make it fire.)

 so all this trouble of non-canonical demands just to give some bit of
 information to `worthSplittingFun`, which can probably get this
 information from  `tryWW`, which knows whether the type really is a
 product type (and not a type variable that was a product type in one
 branch of a case of the body)? Or are there likely other reasons to keep
 `UProd(Used)` instead of `UProd`?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8569#comment:7>
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