[GHC] #13851: Change in specialisation(?) behaviour since 8.0.2 causes 6x slowdown

[GHC]

#13851: Change in specialisation(?) behaviour since 8.0.2 causes 6x slowdown
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        Reporter:  mpickering        |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1-rc2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * cc: simonpj (added)


Comment:

 The bulk of the increase in runtime is due to
 2effe18ab51d66474724d38b20e49cc1b8738f60 (The Early Inline Patch):

 {{{
 Commit 55efc9718b520ef354e32c15c4b49cdfecce412f (Combine identical case
 alternatives in CSE)
 -----
 $ time ./MultiBench2

 real    0m2.786s
 user    0m2.784s
 sys     0m0.000s

 Commit 2effe18ab51d66474724d38b20e49cc1b8738f60 (The Early Inline Patch)
 -----
 $ time ./MultiBench2

 real    0m11.861s
 user    0m11.816s
 sys     0m0.052s
 }}}

 (I'm not sure yet what contributes to the other 0.5 seconds in runtime
 increase.)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13851#comment:3>
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