[GHC] #8836: ghc 7.6.3 (Linux) hangs on -O2

[GHC]

#8836: ghc 7.6.3 (Linux) hangs on -O2
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       Reporter:  tsuraan     |             Owner:
           Type:  bug         |            Status:  new
       Priority:  normal      |         Milestone:
      Component:  Compiler    |           Version:  7.6.3
       Keywords:              |  Operating System:  Unknown/Multiple
   Architecture:              |   Type of failure:  GHC doesn't work at all
  Unknown/Multiple            |         Test Case:
     Difficulty:  Unknown     |          Blocking:
     Blocked By:              |
Related Tickets:              |
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 I haven't had any luck finding a minimal test case for this, but the
 following replicates the issue on my two Linux machines running ghc 7.6.3:

 git clone https://github.com/tsuraan/optimal-blocks
 cd optimal-blocks
 git checkout bceee69f9f03d2e559f96cdf58412ada09c96a8c
 cabal sandbox init
 cabal install --only-dependencies
 cabal configure
 cabal build

 Cabal build will successfully build Algorithm.OptimalBlocks.SipHash and
 Algorithm.OptimalBlocks.BuzzHash, and it will attempt to build
 Algorithm.OptimalBlocks, but it will hang forever, using 100% of a single
 core. I have no idea how to debug this, but in
 src/Algorithm/OptimalBlocks.hs, if you replace the "in Blocks (reverse
 rlist) end" with "in Blocks [] bs", it will compile. Also, if that same
 file starts with the line "{-# OPTIONS_GHC -O1 #-}" it will compile.

 This also happens on my Mac running OSX 10.8.5 and ghc 7.4.2 without llvm;
 I have to tweak the .cabal file a little to drop the lower bound on base
 and to get rid of the "-fllvm" flag, but if I do that I see the exact same
 behaviour.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8836>
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