code development

[Matthew Fluet]

> Also, other switches that you will find useful are the -keep,
> -keep-pass, and -diag switches, which save the output of selected
> passes and turn on diagnostic output.  

The currently checked in ssa/simplify.fun will keep .pre.ssa and .post.ssa
versions of ssa passes when you use -keep-pass.  I find this useful for
debugging passes.

-keep dot can also be helpful, if the graphs aren't to big.
Unfortunately, the dot layout doesn't have access to the name of the .ssa
file being produced, so you don't get pre and post versions.  (In fact,
you only get .dot files for the last ssa layout, which is usually the
final ssa program when you use -keep ssa.)