hg grep qqqq in the mercurial repo:
before: 0,859s
after: 0,233s
hg grep somethingwithnomatch in mozilla-central:
before: 51s
after: 19s
This is probably also a tiny bug fix, because the code was looking up
a node for filename pfn on a filelog for filename fn, which are
most of the time the same filename, but don't have to be.
Ignoring performance and the bug fix, the code should have the same
behavior.