The global analysis has quadratic worst-case complexity in the number of
graphs.  At least if alias analysis is disabled anyway, this can be
avoided.

This avoids strangely large positive numbers instead of negative offsets
on x86_64 hosts.

Privously nodes that only had a keep-alive users would be moved up but
never down again.

The problem was that we have to force SSA construction for memory values to
ensure the presence of the Phi[loop] nodes. Previously we did not do it
if we didn't introduce new values.

This fixes firm-testsuite/opt/jumpthreading8.c

This should really fix opt/fehler218.c oddities.

- This should fix some cases where we would not reassociate constants
  because of multiple users and missed address mode patterns for these
  cases.