[GHC] #13623: join points produce bad code for stream fusion

[GHC]

#13623: join points produce bad code for stream fusion
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        Reporter:  choenerzs         |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.2.1-rc1
      Resolution:  fixed             |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime           |            Test Case:
  performance bug                    |  perf/should_runt/T13623
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by choenerzs):

 With ghc 8.2.-rc2 my original program is now fast again. However, compared
 to ghc-8.0.1 it is now necessary to explicitly give {{{-fspec-constr-
 count=100}}} as otherwise I end up with insufficient specializations.

 (The {{{100}}} is rather arbitrary, but the default is definitely not
 enough)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13623#comment:13>
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