[GHC] #5226: <<loop>> with -threaded -feager-blackholing, but only sometimes

[GHC]

#5226: <<loop>> with -threaded -feager-blackholing, but only sometimes
---------------------------------+------------------------------------------
    Reporter:  dreixel           |       Owner:              
        Type:  bug               |      Status:  new         
    Priority:  normal            |   Component:  Compiler    
     Version:  7.1               |    Keywords:              
    Testcase:                    |   Blockedby:              
          Os:  Unknown/Multiple  |    Blocking:              
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown
---------------------------------+------------------------------------------
 While benchmarking the performance of GHC's SMP parallelism, I ran into an
 issue where (rarely) a test would fail with `<<loop>>`. I tried hard to
 reduce this to a single file, which I am attaching to this report.

 To reproduce, compile the program with `--make -threaded -feager-
 blackholing -rtsopts -O1` and run multiple times with `-Nm` with `m>=2`.
 In my case, using `N8` (on a machine with 8 cores), I once got the error
 after 35 tries, but sometimes it takes thousands of attempts. I'm also
 attaching a bash script to compile and run the test repeatedly.

 Tested with current HEAD, built on a Intel Xeon E5320, "perf" settings
 without dynamic linking. But I think I also encountered this behavior in
 GHC 7.0.3.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5226>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler