[GHC] #11160: New exhaustiveness checker breaks ghcirun004

[GHC]

#11160: New exhaustiveness checker breaks ghcirun004
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       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):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * cc: gkarachalias (added)
 * milestone:   => 8.0.1


Old description:

> The new exhaustiveness checker has broken
> `tests/ghci/should_run/ghcirun004`, which now hangs in desugaring. If one
> removes all but a few hundred of `foo`'s equations in the test things
> return to sanity. It appears that the compile time is scaling non-
> linearly with the number of equations,
>
> ||= no. equations =||= compile wall time =||
> || 150             || 0.4 s ||
> || 250  || 0.89 s  ||
> || 300  || 1.22 s  ||
> || 350  || 1.85 s  ||
> || 400  || 2.65 s  ||
> || 500  || 4.86 s  ||
> || 550  || 6.60 s  ||
> || 600  || 8.65 s  ||
> || 650  || 10.27 s ||
> || 700  || 12.84 s ||
> || 1000 || 38.51 s ||

New description:

 The new exhaustiveness checker (8a506104d5b5b71d5640afc69c992e0af40f2213)
 has broken `tests/ghci/should_run/ghcirun004`, which now hangs in
 desugaring. If one removes all but a few hundred of `foo`'s equations in
 the test things return to sanity. It appears that the compile time is
 scaling non-linearly with the number of equations,

 ||= no. equations =||= compile wall time =||
 || 150  || 0.4 s ||
 || 250  || 0.89 s  ||
 || 300  || 1.22 s  ||
 || 350  || 1.85 s  ||
 || 400  || 2.65 s  ||
 || 500  || 4.86 s  ||
 || 550  || 6.60 s  ||
 || 600  || 8.65 s  ||
 || 650  || 10.27 s ||
 || 700  || 12.84 s ||
 || 1000 || 38.51 s ||

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11160#comment:1>
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