[MLton] question on closure-convert.fun

[Matthew Fluet]

> > These extraneous assignments will be killed off by the removeUnused
> > pass if they are truly unused in the rest of the program.
> 
> If you add the assignments as global statements in the argument to
> Ssa.shrinkFucntion, won't they just not appear in the output
> (i.e. "blocks")?

No, you misunderstand what I was proposing.  Instead of:

                       Ssa.Exp.Tuple vs =>
                          if Vector.equals(vars, vs, Var.equals)
                             then ()
                          else Error.bug "shrinker didn't simplify right"

have

                       Ssa.Exp.Tuple vs =>
                          if Vector.length vars = Vector.length vs
                             then vs
                          else Error.bug "shrinker didn't simplify right"

and

                 val rebinds =
                    Vector.keepAllMapi
                    (vs, fn (i, v) =>
                     if Var.equals (v, Vector.sub (vars, i))
                        then NONE
                        else SOME (Ssa.Statement.T 
                                   {exp = Ssa.Exp.Var v,
                                    ty = Vector.sub (tys, i),
                                    var = SOME (Vector.sub (vars, i))}))

That is, if we see that the shrinker determined that a variable was equal 
to another variable, simply rebind the eliminated variable.