[GHC] #12798: LLVM seeming to over optimize, producing inefficient assembly code...

[GHC]

#12798: LLVM seeming to over optimize, producing inefficient assembly code...
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        Reporter:  GordonBGood       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler (LLVM)   |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by GordonBGood):

 So you are saying we need to both force the evaluation of "twos" '''and'''
 run a newer version of LLVM (which we can't do with GHC version 8.0.1) in
 order to get the desired output but that the forced evaluation of "twos"
 would not be necessary if HEAD did not have a regression as to this
 optimization?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12798#comment:2>
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