[GHC] #15349: fixST is a bit wrong

[GHC]

#15349: fixST is a bit wrong
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        Reporter:  dfeuer            |                Owner:  dfeuer
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Core Libraries    |              Version:  8.5
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by lerkok):

 Update: I cannot replicate Arseniy's example with GHC 8.4.2. He says that
 he's observing it on GHC 8.2.2; but I don't have that version lying around
 to replicate.

 With 8.4.2, Arseniy's example produces 0 with no-eager-blackholing, and
 <<loop>> with eager-blackholing; so it's about the same as with David's
 original example in terms of brokenness.

 So, something got fixed between 8.4.2 and 8.2.2 that the seg-fault
 disappeared. This doesn't mean Arseniy's example can't be replicated on
 8.4.2. I think the next step should be to replicate that on latest GHC and
 decide from there. (Or, if we can't replicate, figure out what got it
 fixed.)

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15349#comment:5>
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