[GHC] #11161: New exhaustiveness checker breaks concurrent/prog001

[GHC]

#11161: New exhaustiveness checker breaks concurrent/prog001
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.0.1
          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:
  concurrent/prog001                 |
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 The new exhaustiveness checker appears to allocate until the machine runs
 out of memory while compiling the `concurrent/prog001` testcase. In
 particular it stalls while desugaring the `Thread` module. The fact that
 this module contains non-trivial pattern matching, coupled with the
 compiler gets stuck in `Desugar`, and the fact that I've noted other
 performance issues with the new exhaustiveness checker (see #10711) leads
 me to believe that this patch is to blame.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11161>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler