[GHC] #12899: ghc panics at random places with -jX

[GHC]

#12899: ghc panics at random places with -jX
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           Reporter:  pacak          |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Affected versions: pretty much all the things from early ghc8  until most
 recent.

 Symptoms: Out of 106 clean builds 36 failed with random ghc panic. By
 random I mean no two are alike. There are 525 files in a project and
 compilation goes in parallel with -j8. Other than panic in 21 cases it
 generates type errors (types are perfectly fine and whatever is under
 "with actual type" is something that probably exists in the same file or
 at least in the project itself but totally unrelated to what type an
 expression actually is. And even in those cases where ghc fails at the
 same file it usually results in different panic messages.


 What was checked:

 Stale interface files: No, ghc is told to use a separate build directory
 build system removes it

 bad memory/random file system corruption: No, ghc 7.10 builds the same
 codebase just fine and it also fails on other machines

 strange packages in user package database: No, ghc is told to ignore those

 ghc was reinstalled several times with system package db wiped.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12899>
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