diff -r 2ca116614cfc -r d50677c3bf44 mercurial/revset.py
--- a/mercurial/revset.py	Wed Jul 01 13:14:03 2015 -0700
+++ b/mercurial/revset.py	Thu Jul 02 23:46:18 2015 -0700
@@ -1478,11 +1478,13 @@
     else:
         ps = set()
         cl = repo.changelog
+        up = ps.update
+        parentrevs = cl.parentrevs
         for r in getset(repo, fullreposet(repo), x):
             if r is None:
-                ps.update(p.rev() for p in repo[r].parents())
+                up(p.rev() for p in repo[r].parents())
             else:
-                ps.update(cl.parentrevs(r))
+                up(parentrevs(r))
     ps -= set([node.nullrev])
     return subset & ps