[GHC] #7258: Compiling DynFlags is jolly slow

[GHC]

#7258: Compiling DynFlags is jolly slow
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        Reporter:  simonpj           |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.1
      Resolution:                    |             Keywords:  deriving-perf
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by tdammers):

 So apparently, good shape (linear-ish performance):


 {{{
 D <$> a1 <*> a2 <*> a2 <*> ... <*> aN
 }}}

 Bad shape (exponential-ish performance):

 {{{
 do
   v1 <- a1
   v2 <- a2
   v3 <- a3
   ...
   vN <- aN
   return $ D v1 v2 v3 ... vN
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7258#comment:44>
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