[GHC] #13027: The let/app invariant, evaluated-ness, and reallyUnsafePtrEquality#

[GHC]

#13027: The let/app invariant, evaluated-ness, and reallyUnsafePtrEquality#
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        Reporter:  erikd             |                Owner:  dfeuer
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Building GHC      |            Test Case:
  failed                             |  simplCore/should_compile/T13027
      Blocked By:                    |             Blocking:
 Related Tickets:  #11444            |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * owner:   => dfeuer


Comment:

 * `reallyUnsafePtrEq#`: see comment:15 of #11444.  Phab:D2987 does this
 (thank you David); but it has no test.  (I'm not certain it neeeds one.)

 * `seq#` is mis-named.  It should really be `evaluate#` because it's the
 primop version of `evaluate`:
 {{{
 seq# ::   a -> State# s -> (# State# s, a #)

 evaluate :: a -> IO a
 evaluate a = IO $ \s -> seq# a s -- NB. see #2273, #5129
 }}}
   I don't think it needs any `can_fail` or `has_side_effects` attributes,
 because it is totally constrained by the threaded state.  I wish I could
 be 100.00% certain, but that's how it looks to me.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13027#comment:33>
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