ssa restore

[Stephen Weeks]

> Something else to keep in mind for the exceptions paper:
> without needing to worry about HandlerPush/Pops, I would just have
> rewriteTransfer map route over all the labels.  Now, with the old version
> of route, this would have given each nontail call at a handler with phi
> arguments a different route block.  Nothing in the simplification pipeline
> would eliminate these alpha-equivalent blocks, so implementHandlers would
> probably do something costly, particularly in terms of space.

Maybe this should go on the common-block todo list?