[GHC] #14519: Exponential runtime performance regression in GHC 8.2 + Data.Text.Lazy + Text.RE.TDFA

[GHC]

#14519: Exponential runtime performance regression in GHC 8.2 + Data.Text.Lazy +
Text.RE.TDFA
-------------------------------------+-------------------------------------
        Reporter:  ntc2              |                Owner:  tdammers
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime           |            Test Case:
  performance bug                    |  https://github.com/ntc2/ghc-8.2.1
                                     |  -regex-lazy-text-
                                     |  bug/tree/07b7bb32c6e90e8f2d2eada4b59943f37e632d53
      Blocked By:                    |             Blocking:
 Related Tickets:  #13745, #14564    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by tdammers):

 > I would urge you to build the program and libraries with -ticky and see
 which function is getting executed a lot. The advantage of -ticky is that
 it's guaranteed not to affect optimisation or indeed anything. It just
 logs what happens.

 That's actually exactly what I'm doing right now. A comparison of running
 two regular expressions such that one is fast (`^[^.]d`) and the other is
 slow (`^def`) shows that all the metrics are the same, or nearly the same,
 except for ALLOC_PRIM_gds (from 669 up to 1801526) and ALLOC_PRIM_ctr
 (from 371392 up to 9325581456).

 I should probably dig a bit deeper from here.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14519#comment:11>
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