[GHC] #7944: GHC goes into an apparently infinite loop at -O2

[GHC]

#7944: GHC goes into an apparently infinite loop at -O2
-------------------------------------+-------------------------------------
              Reporter:  bos         |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.6.3
            Resolution:              |         Keywords:
      Operating System:  MacOS X     |     Architecture:  x86_64 (amd64)
       Type of failure:  Compile-    |       Difficulty:  Unknown
  time crash                         |       Blocked By:
             Test Case:              |  Related Tickets:  5550
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
Changes (by thomie):

 * status:  infoneeded => new


Comment:

 I don't think this is fixed yet.


 Steps to reproduce (with a quick build of today's ghc master in directory
 ~/ghc-build, on Linux):

 {{{
 cabal install --with-ghc=ghc-build/inplace/bin/ghc-stage2 vector
 git clone https://github.com/thomie/inttable
 cd inttable
 ~/ghc-build/inplace/bin/ghc-stage2 -O2 -v3 --make Repro

 }}}

 This last step freezes after about 1 second, with final output:

 {{{
 *** SpecConstr:
 Result size of SpecConstr
 }}}

 CPU is at 100%, until I kill it after a few minutes. Contrary to Brian's
 observation, I do see an increase in memory usage over time. I get the
 same results when using ghc-7.8.3 instead of current ghc master.


 I had to make a small change to Bryan's `inttable` repository (hide some
 imports from base). See the mentioned github url.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7944#comment:5>
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