ancestor: caching the parent list to improve performance...
ancestor: caching the parent list to improve performance
When computing the DAG depth, we walk through all ancestors: this commit adds
memoization during that first step. Then, the memorized parents are fetched
from a dict instead of calling parents() on each vertex.
This tweak, according to Kcachegrind, improves ancestor() performance by 16%
when cloning a big repository.