How to debug ssa optimizer

[Richard Kenner]

    This is buried pretty deeply.  When implementing check_pointer_types_r,
    I gave up and allowed it.  Ideally we'd generate &array[0] instead.

I was just about to add a test to check_pointer_types_r to disallow it.
I think it's not that hard to fix and otherwise the ssa optimizers have to
make sure they don't make things worse (and one of my changes is causing
problems in that area).