[GHC] #11989: Performance bug reading large-exponent float without explicit type

[GHC]

#11989: Performance bug reading large-exponent float without explicit type
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           Reporter:  bpearlmutter   |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Runtime        |           Version:  7.10.3
  System                             |
           Keywords:                 |  Operating System:  Linux
       Architecture:  x86_64         |   Type of failure:  Runtime
  (amd64)                            |  performance bug
          Test Case:  1e1000000 ::   |        Blocked By:
  (RealFloat a => a)                 |
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{
 $ time echo '1e700000' | ghci
 GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
 Prelude> Infinity
 Prelude> Leaving GHCi.

 real    1m25.799s
 user    0m20.828s
 sys     0m9.624s

 $ time echo '1e700000::Double' | ghci
 GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
 Prelude> Infinity
 Prelude> Leaving GHCi.

 real    0m0.196s
 user    0m0.120s
 sys     0m0.032s

 $ time echo 1e-800000 | ghci
 GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
 Prelude> Killed

 real    2m8.879s
 user    0m6.684s
 sys     0m10.256s
 }}}
 Giving an explicit type `(RealFloat a => a)` doesn't make any difference.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11989>
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