[GHC] #11160: New exhaustiveness checker breaks ghcirun004

[GHC]

#11160: New exhaustiveness checker breaks ghcirun004
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:
          Component:  Compiler       |           Version:  7.10.2
           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:
-------------------------------------+-------------------------------------
 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 ||

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11160>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler