[GHC] #8131: T7571 with WAY=llvm fails, but not WAY=optllvm

[GHC]

#8131: T7571 with WAY=llvm fails, but not WAY=optllvm
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        Reporter:  thoughtpolice              |            Owner:  rwbarton
            Type:  bug                        |           Status:  new
        Priority:  high                       |        Milestone:
       Component:  Compiler                   |          Version:  7.7
      Resolution:                             |         Keywords:
Operating System:  Unknown/Multiple           |     Architecture:
 Type of failure:  None/Unknown               |  Unknown/Multiple
       Test Case:  llvm/should_compile/T8131  |       Difficulty:  Unknown
        Blocking:                             |       Blocked By:
                                              |  Related Tickets:
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Comment (by rwbarton):

 This patch is basically done.

 I preserved the four-argument syntax for `prim %memcpy` etc. in `.cmm`
 files. This was trickier than I expected due to the tying-the-knot
 technique used to resolve Cmm names during parsing: we can't pattern-match
 on the alignment `CmmExpr` argument (to check whether it is a `CmmLit`)
 while producing the `MO_MemCpy` call. My workaround was to fail in a
 "pure" way, with `pprPgmError`, producing a rather ugly error message. A
 better solution here is welcome. But, this only affects compilation of
 `.cmm` files so it's not so bad if the edges are a bit rough IMO.

 Here is the patch for review, particularly of that parsing bit but also
 generally.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8131#comment:4>
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