fix OP_PHI usage in try_to_simplify_bb() only when non-bogus

fix OP_PHI usage in try_to_simplify_bb() only when non-bogus

Currently, sparse method of conversion to SSA form, doesn't
place phi-nodes at the dominance frontier but often place them
'lower' where the corresponding 'value' is needed.
This, in itself create all sort of problems. One of these
problems is that it is then quite common for an OP_PHI
to contains less 'sources' than it has parents. This is wrong
has phi-nodes represent the 'join' a value can have from each
of the incoming paths/parents.

This situation can't be given a sensible semantic and any
attempt to try some optimization involving the phi-nodes and
their sources are bound to fail.

Temporary workaround this in try_to_simplify_bb() by simply
checking if the number of parents and the number of phi-sources
match and avoid to make this simplification if they don't.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>