[GHC] #15226: GHC doesn't know that seq# produces something in WHNF

[GHC]

#15226: GHC doesn't know that seq# produces something in WHNF
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4796
       Wiki Page:                    |
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Comment (by dfeuer):

 Replying to [comment:14 simonpj]:
 > > So if we do a binder swap, we should do it for all the variables the
 scrutinee is strict
 >
 > This is a bridge too far!  Strictness analysis will work this out, I
 think.  Eg that `let e` will turn into a case.

 I don't think so. `seq#` is intentionally lazy in its argument, to allow
 explicit ordering in an `IO` context. This seems pretty important in
 combination with `spark#`, for example.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15226#comment:15>
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