[GHC] #7450: Regression in optimisation time of functions with many patterns (6.12 to 7.4)?

[GHC]

#7450: Regression in optimisation time of functions with many patterns (6.12 to
7.4)?
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        Reporter:  iustin            |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.6.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by bgamari):

 Ahh, yes, sorry, the above repository is at this point really just a
 couple of scripts for characterising the problem.

 `-dshow-passes` points at the specializer being much of the issue. Take
 the case of a 1000 constructor ADT. With GHC from `master`, the
 compilation takes roughly 75 seconds on my laptop. Of this it seems
 roughly 20 seconds is spent in the specialiser, and another 20 seconds are
 spent in the assembler. Otherwise the rest of the time is split between
 various simplifier iterations, with no single iteration taking more than a
 couple of seconds.

 If I disable specialisation the compilation time drops to 52 seconds, with
 the largest portion of this being a 7 second simplifier iteration.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7450#comment:12>
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