[GHC] #13518: CMM compiles with 8.0.2, fails with git HEAD

[GHC]

#13518: CMM compiles with 8.0.2, fails with git HEAD
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        Reporter:  erikd             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by erikd):

 Wow, something really subtle is going on. Pasting your exact code made it
 work. Using `FLOAT_STACK_WDS` set to `2` to get stack alignment correct
 didn't.

 It even passes the test! Just need to clean it up and get it up on Phab.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13518#comment:8>
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