[GHC] #13745: Investigate compile-time regressions in regex-tdfa-1.2.2

[GHC]

#13745: Investigate compile-time regressions in regex-tdfa-1.2.2
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      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 RyanGlScott):

 I've attached a minimized version of `regex-tdfa-1.2.2` with no external
 dependencies. Moreover, the slowdown in GHC 8.2 seems primarily
 concentrated at the `*Engine` files, so I only included what was necessary
 to support one of them. Here are the times that I got:

 {{{
 $ time /opt/ghc/8.0.2/bin/ghc -O2 -fforce-recomp
 TextRegexTDFANewDFAEngine_FA.hs
 real    0m10.139s
 user    0m9.996s
 sys     0m0.116s

 $ time /opt/ghc/8.2.1/bin/ghc -O2 -fforce-recomp
 TextRegexTDFANewDFAEngine_FA.hs
 real    0m18.072s
 user    0m17.912s
 sys     0m0.156s
 }}}

 The `TextRegexTDFANewDFAEngine_FA.hs` file in particular is what is
 contributing to the difference in time, as all other modules take about
 the same time to compile on 8.0.2 and 8.2.1-rc2.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13745#comment:3>
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