[MLton] arith shrinking & bit fiddling

[Stephen Weeks]

> Without it, we don't simplify overflow checking operations like:
>  0 - x
>  ~1 * x
> 
> 
> 2) Does anyone know an efficient way of doing overflow checking for signed
> negation in assembly?  Note that defining:
>   val Int64.~ =
>                if detectOverflow
> 		  then (fn i: int => if i = minInt'
> 					then raise Overflow
> 				     else ~? i)
> 	       else ~?
> is o.k., but the simplification above will introduce Int64_negCheck even
> if it doesn't appear in the source program.

You mean for  0 - x ---> ~x?  I don't understand why this is bad.
It's replacing Int64_subCheck with Int64_negCheck.

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