[GHC] #1016: Avoidance of unaligned loads is overly conservative

[GHC]

#1016: Avoidance of unaligned loads is overly conservative
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    Reporter:  igloo     |       Owner:         
        Type:  task      |      Status:  new    
    Priority:  normal    |   Milestone:  6.8    
   Component:  Compiler  |     Version:  6.6    
    Severity:  normal    |    Keywords:         
  Difficulty:  Unknown   |    Testcase:  N/A    
Architecture:  Unknown   |          Os:  Unknown
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On alpha, mips, mipsel and arm we do loads in a way that is safe even if
 they are unaligned (see `cLoad` in `compiler/cmm/PprC.hs`). We need this
 when, for example, we read things with `indexInt16OffAddr#` from `Addr#`s
 in alex-generated lexers, but most of the time we know that the address is
 aligned appropriately so loads are slower than they need be.

 A better way to do this would be to make Load a `MachOp` parameterised by
 whether it's known to be aligned or not. Likewise, Store should be a
 `CallishMachOp`.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1016>
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