revset: remove existence check from min() and max() min() and max() would first do an existence check. Unfortunately existence checks can be slow in certain situations (like if the smartset is a list, and quickly iterable in both ascending and descending directions, then doing an existence check will start from the bottom, even if you want to check the max()). The fix is to not do the check, and just handle the error if it happens. In a large repo, this speeds up: hg log -r 'max(parents(. + .^) - (. + .^) & ::master)' from 3.5s to 0.85s. That revset is contrived and just for testing. In our real case we used 'bundle()' in place of '. + .^' Interesting perf numbers for the revset benchmarks: max(draft() and ::tip) => 0.027s to 0.0005s max(author(lmoscovicz)) => 2.48s to 0.57s min doesn't show any perf changes, but changing it as well will prevent a perf regression in my next patch. Result from revset benchmark revset #0: draft() and ::tip min max 0) 0.001971 0.001991 1) 0.001965 0.000428 21% revset #1: ::tip and draft() min max 0) 0.002017 0.001912 1) 0.001896 94% 0.000421 22% revset #2: author(lmoscovicz) min max 0) 1.049033 1.358913 1) 1.042508 0.319824 23% revset #3: author(lmoscovicz) or author(mpm) min max 0) 1.042512 1.367432 1) 1.019750 0.327750 23% revset #4: author(mpm) or author(lmoscovicz) min max 0) 1.050135 0.324924 1) 1.070698 0.319913 revset #5: roots((tip~100::) - (tip~100::tip)) min max 0) 0.000671 0.001018 1) 0.000605 90% 0.000946 92% revset #6: roots((0::) - (0::tip)) min max 0) 0.149714 0.152369 1) 0.098677 65% 0.100374 65% revset #7: (20000::) - (20000) min max 0) 0.051019 0.042747 1) 0.035586 69% 0.016267 38%

--- a/mercurial/revset.py	Fri Sep 18 17:23:10 2015 -0700
+++ b/mercurial/revset.py	Sun Sep 20 19:27:53 2015 -0700
@@ -1387,10 +1387,14 @@
     Changeset with highest revision number in set.
     """
     os = getset(repo, fullreposet(repo), x)
-    if os:
+    try:
         m = os.max()
         if m in subset:
             return baseset([m])
+    except ValueError:
+        # os.max() throws a ValueError when the collection is empty.
+        # Same as python's max().
+        pass
     return baseset()
 
 def merge(repo, subset, x):
@@ -1426,10 +1430,14 @@
     Changeset with lowest revision number in set.
     """
     os = getset(repo, fullreposet(repo), x)
-    if os:
+    try:
         m = os.min()
         if m in subset:
             return baseset([m])
+    except ValueError:
+        # os.min() throws a ValueError when the collection is empty.
+        # Same as python's min().
+        pass
     return baseset()
 
 def modifies(repo, subset, x):