[GHC] #13817: Simplifier and SpecConstr performance regression with 8.2.1

[GHC]

#13817: Simplifier and SpecConstr performance regression with 8.2.1
-------------------------------------+-------------------------------------
           Reporter:  albertov       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1-rc1
           Keywords:                 |  Operating System:  Linux
       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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 A propietary application I've upgraded to compile with 8.2.1-rc1 makes GHC
 manifest a performance regression when producing optimized ({{{-O2}}})
 code.

 After a crude analysis of a compile log produced with {{{-show-passes}}}
 it appears that the biggest slowdown is in the Simplifier and SpecConstr
 phases when compiling the "main" modules.

 Theres a conversation at GHC Users with more details:
 https://mail.haskell.org/pipermail/glasgow-haskell-
 users/2017-June/026543.html. The data, the results and the script to to
 analyse it live at:
 https://gist.github.com/albertov/145ac5c01bfbadc5c9ff55e9c5c2e50e

 I'll try to update this ticket with a way to to reproduce it as soon as I
 can (if I can)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13817>
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