# HG changeset patch
# User Boris Feld <boris.feld@octobus.net>
# Date 1544089145 -3600
# Node ID f960c51eebf32499f9f8c592b25f1a272a280e5a
# Parent  74ee5ff1e81c46ec2acb513eedba5a6742b5f055
delta: filter nullrev out first

When picking a potential candidate, we filter them on various criteria. The
"different from nullrev" criteria is very fast to compute and we should
process it first.

diff -r 74ee5ff1e81c -r f960c51eebf3 mercurial/revlogutils/deltas.py
--- a/mercurial/revlogutils/deltas.py	Thu Dec 06 10:38:30 2018 +0100
+++ b/mercurial/revlogutils/deltas.py	Thu Dec 06 10:39:05 2018 +0100
@@ -633,6 +633,10 @@
                             or deltalength(rev))):
                 tested.add(rev)
                 rev = deltaparent(rev)
+            # no need to try a delta against nullrev, this will be done as a
+            # last resort.
+            if rev == nullrev:
+                continue
             # filter out revision we tested already
             if rev in tested:
                 continue
@@ -640,10 +644,6 @@
             # filter out delta base that will never produce good delta
             if deltas_limit < revlog.length(rev):
                 continue
-            # no need to try a delta against nullrev, this will be done as a
-            # last resort.
-            if rev == nullrev:
-                continue
             # no delta for rawtext-changing revs (see "candelta" for why)
             if revlog.flags(rev) & REVIDX_RAWTEXT_CHANGING_FLAGS:
                 continue