[GHC] #14619: Output value of program changes upon compiling with -O optimizations

[GHC]

#14619: Output value of program changes upon compiling with -O optimizations
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        Reporter:  sheaf             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Windows           |         Architecture:  x86_64
 Type of failure:  Incorrect result  |  (amd64)
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Phyx-):

 However, using the newer toolchain with the same Haskell libraries as
 before (e.g. base, GHC-prim) etc generates the same wrong result. So It's
 unlikely to be a `mingw-w64` bug. Back to GHC it is.. but likely now
 should look at the code in base.

 I also swapped out GHC-prim from 8.2.2 with the one from head and that
 didn't work. So the difference must be in base? I'm grasping at straws
 here :)

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14619#comment:20>
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