[GHC] #13174: Fix mismatch between unsafeDupablePerformIO and note

[GHC]

#13174: Fix mismatch between unsafeDupablePerformIO and note
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        Reporter:  dfeuer            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Core Libraries    |              Version:  8.1
      Resolution:                    |             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 rwbarton):

 Oops, I deleted the reference to the note in
 https://phabricator.haskell.org/D1103, but failed to remove the note
 itself. Same story with the note `[unsafeDupablePerformIO has a lazy
 RHS]`.

 The lack of NOINLINE is okay because `runRW#` is NOINLINE. I'm not sure
 what the story about strictness was though.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13174#comment:1>
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