[GHC] #10108: Dramatic slowdown with -O2 bytestream and list streams combined.

[GHC]

#10108: Dramatic slowdown with -O2 bytestream and list streams combined.
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        Reporter:  Truman            |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  7.10.2
       Component:  Compiler          |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Linux             |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |  break_in.hs
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by simonpj):

 Please can you say exactly which versions of which libraries are required?
 And the exact command line you used to compile `break_ins.hs`?

 This an awkward one.

 On the one hand, `ghc -O2` should not produce code 3600 time slower than
 `ghc -O`.  On the the other hand, the example depends on two big
 libraries, each of which has lots of rewrite rules that may or may not be
 right.  So there may be nothing wrong with GHC.

 It'd be really helpful if someone (e.g. the library maintainers) could
 investigate, and characterise more clearly what is going on.  The more
 precisely the problem is identified, the more likely that someone will fix
 it.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10108#comment:1>
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