[GHC] #7684: cgrun071 segfaults

[GHC]

#7684: cgrun071 segfaults
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        Reporter:  tibbe          |            Owner:
            Type:  bug            |           Status:  infoneeded
        Priority:  normal         |        Milestone:  7.8.1
       Component:  Compiler       |          Version:  7.7
      Resolution:                 |         Keywords:
Operating System:  MacOS X        |     Architecture:  x86_64 (amd64)
 Type of failure:  Runtime crash  |       Difficulty:  Unknown
       Test Case:  cgrun071       |       Blocked By:
        Blocking:                 |  Related Tickets:
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Comment (by tibbe):

 I chatted a bit with rwbarton about the semantics of these primops. My
 intention is that all the primops work on all input sizes (much like the
 underlying assembly instruction) and the difference is just the number of
 bit we count. The code implements this behavior correctly, if it weren't
 for LLVM misbehaving. The reason I implemented the primops this way is
 that I wanted to avoid the narrowing.

 This means that even if we had a `Word8#` type, the primops would still
 operate on a `Word#`. Does that make sense?

 If so the right fix is to work around the LLVM bug in `popcnt.c`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7684#comment:51>
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