SSA IL

[Matthew Fluet]

> > Well, I just checked in flatten (and checked in redundantTests and
> > loopInvariant earlier today).  That just leaves the shrinker,
> > constantPropagation, useless, and simplifyTypes.  Guess I'm all done. ;)
> 
> Feel free to start on the other 3.  You're doing great!  I'm still
> embroiled in the shrinker, which I hope will be in good enough shape
> for testing by tomorrow, and checked in by Thursday.

O.k.  Now I'm really all done.  I'm not going to write new SSA passes
until the shrinker is done.