[GHC] #9122: Make Lint check for bad uses of `unsafeCoerce`

[GHC]

#9122: Make Lint check for bad uses of `unsafeCoerce`
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        Reporter:  simonpj           |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      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 simonpj):

 The rules are documented with `unsafeCoerce`,
 [http://www.haskell.org/ghc/docs/latest/html/libraries/ghc-prim-0.3.1.0
 /GHC-Prim.html#v:unsafeCoerce-35- here].

 It's pretty much guaranteed that coercing from, say `Int#` to `Int` will
 give rise to serious problems.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9122#comment:2>
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