[PATCH] revset-_ancestor: use & instead of filter

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1412107434 18000
#      Tue Sep 30 15:03:54 2014 -0500
# Node ID cd1d993fd93096dbb7886b6cba28b57fff100b3b
# Parent  840be5ca03e1db16ba994e55597771c418166c97
revset-_ancestor: use & instead of filter

The & operation is more likely optimised.

::10
before) wall 0.028189 comb 0.030000 user 0.030000 sys 0.000000 (best of 100)
after)  wall 0.001050 comb 0.000000 user 0.000000 sys 0.000000 (best of 2326)

::tip
before) wall 0.081132 comb 0.080000 user 0.080000 sys 0.000000 (best of 100)
after)  wall 0.055418 comb 0.050000 user 0.050000 sys 0.000000 (best of 100)

diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -345,11 +345,11 @@ def ancestor(repo, subset, x):
 def _ancestors(repo, subset, x, followfirst=False):
     heads = getset(repo, spanset(repo), x)
     if not heads:
         return baseset()
     s = _revancestors(repo, heads, followfirst)
-    return subset.filter(s.__contains__)
+    return subset & s
 
 def ancestors(repo, subset, x):
     """``ancestors(set)``
     Changesets that are ancestors of a changeset in set.
     """