[GHC] #10090: Building ghc with "make -j12" gives different ABI hashes for base to "make -j8"

[GHC]

#10090: Building ghc with "make -j12" gives different ABI hashes for base to "make
-j8"
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        Reporter:  juhpetersen       |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Build System      |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Description changed by juhpetersen:

Old description:

> While building ghc-7.8.4 for Fedora 22 (devel) I found that doing highly
> parallel make builds of ghc affects the ABI hash of base, etc.
>
> The threshold seems to be between -j8 and -j12, which likely changes the
> build order of some modules causes changes to ABI hashes.
>
> While it is not hard to workaround, it is not really nice so it would be
> good to track this down IMHO.  I haven't seen this kind of issue since
> 7.4.2 anyway so it may be an indirect buildsystem "regression" with
> ghc-7.8?

New description:

 While building ghc-7.8.4 for Fedora 22 (devel) I found that doing highly
 parallel make builds of ghc affects the ABI hash of base, etc.

 The threshold seems to be between -j8 and -j12, which likely changes the
 build order of some modules causing changes to ABI hashes.

 While it is not hard to workaround, it is not really nice so it would be
 good to track this down IMHO.  I haven't seen this kind of issue since
 7.4.2 anyway so it may be an indirect buildsystem "regression" with
 ghc-7.8?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10090#comment:1>
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