Step2: Pre-clustering
Goal: Reduce the number of procedures for subsequent N-way assignment by merging procedures whose separation among parts would never represent good solution.
Different from granularity step: procedures being clustered here may not be such that they could exlined into single new procedure. I.e. calls to theses procedure are non-adjacent.
Different from N-way assignment: each cluster does not represent a processor and therefore can not be guided by direct design metrics estimates.