[GHC] #11822: Pattern match checker exceeded (2000000) iterations

[GHC]

#11822: Pattern match checker exceeded (2000000) iterations
-------------------------------------+-------------------------------------
           Reporter:  j.waldmann     |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1-rc3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:  x86_64         |   Type of failure:  Compile-time
  (amd64)                            |  performance bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 graphviz seems a nice benchmark (not too large, few dependencies) that
 highlights compiler performance problems on "trivial" source code
 (cf. https://hackage.haskell.org/package/graphviz-2999.18.0.2/docs/src
 /Data-GraphViz-Attributes-Complete.html#sameAttribute)

 Compilation of Compiling Data.GraphViz.Attributes.Colors.X11 and
 Data.GraphViz.Attributes.Values takes >= 1 second each, and the following
 happens:

 {{{
 cabal install graphviz-2999.18.0.2 --allow-newer

 ...

 [17 of 31] Compiling Data.GraphViz.Attributes.Complete (
 Data/GraphViz/Attributes/Complete.hs, dist/dist-sandbox-
 e6f2c124/build/Data/GraphViz/Attributes/Complete.o )

 Data/GraphViz/Attributes/Complete.hs:1013:1: warning:
     Pattern match checker exceeded (2000000) iterations in
     an equation for ‘sameAttribute’. (Use -fmax-pmcheck-iterations=n
     to set the maximun number of iterations to n)
 }}}

 I do welcome that ghc emits this warning - I expect you want its occurence
 to be reported as a bug?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11822>
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