[GHC] #9233: Compiler performance regression

[GHC]

#9233: Compiler performance regression
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        Reporter:  augustss      |            Owner:
            Type:  bug           |           Status:  new
        Priority:  low           |        Milestone:
       Component:  Compiler      |          Version:  7.8.2
      Resolution:                |         Keywords:
Operating System:  Windows       |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown  |       Difficulty:  Unknown
       Test Case:                |       Blocked By:
        Blocking:                |  Related Tickets:
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Comment (by rwbarton):

 I profiled GHC and ran it on Lennart's sample code. It spent quite a lot
 of time, 23.4% in `coercionKind.go`. Further investigation seemed to
 indicate that most of that time was spent in the `TyConAppCo` case, when
 called from `coercionRole`. I made the Functor and Applicative (and other)
 instances of `Pair` lazy in the pair, trying to avoid traversing the
 entire coercion when we only need the outermost type constructor. It did
 speed up the compilation significantly, from 25 seconds to 18 seconds:

 {{{
 # current HEAD
 <<ghc: 81626230952 bytes, 3494 GCs, 71837424/232400704 avg/max bytes
 residency (28 samples), 591M in use, 0.00 INIT (0.00 elapsed), 17.98 MUT
 (18.23 elapsed), 6.38 GC (6.38 elapsed) :ghc>>
 # with lazy Pair instances
 <<ghc: 42510020272 bytes, 2493 GCs, 71633789/232686656 avg/max bytes
 residency (28 samples), 591M in use, 0.00 INIT (0.00 elapsed), 12.00 MUT
 (12.26 elapsed), 6.06 GC (6.06 elapsed) :ghc>>
 }}}

 However, it had almost no effect on compile allocations for any program in
 nofib. Perhaps the bad behavior is triggered by large list or record
 literals.

 There must be other regressions, since 7.6.3 takes only 9 seconds on my
 system. Also, I note that the object files produced by 7.8 or HEAD for
 Flags and Options are about 25% larger than those produced by 7.6.3.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9233#comment:10>
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