[GHC] #11239: GHC HEAD: cannot bootstrap HEAD with HEAD

[GHC]

#11239: GHC HEAD: cannot bootstrap HEAD with HEAD
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           Reporter:  heisenbug      |             Owner:
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:  8.0.1
          Component:  Compiler       |           Version:  7.11
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Building GHC
  Unknown/Multiple                   |  failed
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The first invocation of a freshly built `inplace/bin/deriveConstants`
 hangs when I am bootstrapping HEAD with HEAD.

 Last proven good git revision: d25f3c076e6c47bc7c8d0d27e724a3ad2b7d7399

 Broken revision: 0dd61fe72144a829a9e5bb87a1094244e53cdebb

 There are only a few revisions in between. Notably:
 {{{
 commit 8a506104d5b5b71d5640afc69c992e0af40f2213
 Author: George Karachalias <george.karachalias at gmail.com>
 Date:   Thu Dec 3 12:57:19 2015 +0100

     Major Overhaul of Pattern Match Checking (Fixes #595)
 ...
 }}}
 Incidentally there are a few known performance regressions from that
 commit, so maybe the bootstrap process is bitten by it.
 I am not sure whether `deriveConstants` really hangs or just takes ages to
 complete.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11239>
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