[GHC] #11095: -O0 -g slows GHC down on list literals (compared to -O0 without -g)

[GHC]

#11095: -O0 -g slows GHC down on list literals (compared to -O0 without -g)
-------------------------------------+-------------------------------------
        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      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):  phab:D3001
       Wiki Page:                    |
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Changes (by niteria):

 * differential:   => phab:D3001


Comment:

 This still reproduces on GHC HEAD.

 @slyfox: Thanks for the profile, it was helpful to know where to look.

 phab:D3001 optimizes the hot `tickishContains` function a bit.

 I've experimented with this a bit and here's what I found:
 * 45 `()` literals generates 20929 `mkTick'` calls and 1371 `mkTick`
 calls.
 * 90 `()` literals generates 143074 `mkTick'` calls and 4746 `mkTick`
 calls.
 * 135 `()` literals generates 457594 `mkTick'` calls and 10146 `mkTick`
 calls.

 In the 45 case almost all of the calls come from `wrapTicks`, and out of
 these most of them (~20k) come from:

 {{{
 wrapBind t (NonRec binder rhs) = NonRec binder (mkTick t rhs)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11095#comment:4>
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