[GHC] #8372: enable -dcmm-lint by default for .cmm input files

[GHC]

#8372: enable -dcmm-lint by default for .cmm input files
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       Reporter:  rwbarton          |             Owner:
           Type:  feature request   |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.7
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 I'm finding it's quite easy to write `.cmm` files with subtle errors that
 cause ghc to emit code that wasn't what I wanted! For example, I wrote a
 comparison between two arguments of different integer sizes and the code
 generator picked the wrong size. After tracking down the bug, I tried
 `-dcmm-lint` and it caught my error right away.

 It makes sense not to have `-dcmm-lint` enabled by default for Cmm
 produced from Stg, but I've seen here on the GHC wiki that `-dcmm-lint` is
 advised for hand-written `.cmm` files. But `integer-gmp`, and probably
 many other packages, don't build `.cmm` files with `-dcmm-lint`. Is there
 a reason we can't/shouldn't just make it the default?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8372>
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