[GHC] #14982: LLVM default -mcpu setting inhibits customization

[GHC]

#14982: LLVM default -mcpu setting inhibits customization
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        Reporter:  tommd             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.2
       Component:  Compiler (LLVM)   |              Version:  8.4.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by angerman):

 The code in question pulls the `mcpu` (and `mattr`) from the new `llvm-
 targets` file. As such a hack around it right now would be to just modify
 the `llvm-targets` file. This however is a rather ugly hack as it would
 apply the logic globally.

 I guess we could just, as suggested, trop the `mcpu` from `llc` if a
 custom one is given. I'm not sure how to handle `mattr` though.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14982#comment:2>
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