[GHC] #12028: Large let bindings are 6x slower (since 6.12.x to 7.10.x)

[GHC]

#12028: Large let bindings are 6x slower (since 6.12.x to 7.10.x)
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           Reporter:  tommd          |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 See the attached somewhat reduced version of the main (manually unrolled)
 portion of an MD5 implementation taken from PureMD5.  It used to compile
 in about 200ms, which is already bad enough, but now takes 1200 ms (ghc
 6.12.3 to ghc 7.10.3 using -O2).  I'd like to note that in my light
 testing the UNPACK pragma accounts for 400ms of this delta.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12028>
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