[MLton] Performance of Real.toInt

[Ryan Newton]

Hello,

My compiler uses either SML or C as a backend.  There's one
application right now where SML/MLton is getting crushed.  It's a
computer vision app where the core computation involves updating
histograms -- picking a location in some space (inexact) and then
discretizing (truncating a floating point number).

The truncation in the source language happens by converting the floats
to ints.  Under MLton I generate code like this:

  (Real64.toInt IEEEReal.TO_ZERO (var_tmpsmp_77))

But it performs very poorly.  I haven't researched this, but if I had
to guess, I'd bet this is because mlton is implementing some more
semantically meaningful notion than C casts.  Nevertheless, is there
any inexpensive way to ape the behavior one gets from (int)x in C?

-Ryan