[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:  closed
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.1
      Resolution:  invalid           |             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):

 > I don't understand this comment: the Haskell stack is only word-aligned
 and the argument to reserve is in words, so it cannot unalign the stack.

 On 32 but systems, `Double` is two words and on 64 bit systems, `Float` is
 half a word. I did have some CPP which tried to account for this and that
 is what was breaking when I first tries @slyfox's `TO_W_` technique.

 > I believe I32 w in the formal argument list is meaningless

 So how does one express a `Word32` in a portable way in CMM?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13518#comment:12>
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