[GHC] #10818: GHC 7.10.2 takes much longer to compile some packages

[GHC]

#10818: GHC 7.10.2 takes much longer to compile some packages
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        Reporter:  kazu-yamamoto     |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
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 simonpj):

 I'm still puzzled by the ''quadrupling'' in compile time describe in the
 Description.  Is that reproducible.  Incrasing from 1.8s to 2.6s seems
 much less dramatic.

 Bisection is great!  I would not have suspected that patch.  Inspecting
 it, I think that perhaps dfuns are specialised after the patch but not
 before.  Try `-dshow-passes` before and after to show code size; and
 `-ddump-rules` to show what specialision rules have been created (at least
 for top level things).  Then worth checking that the extra specialisations
 make sense.

 (I'm assuming that this program does not actually say `-fspecialise-
 aggressively`?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10818#comment:19>
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