perf: add perfbdiff

bdiff shows up a lot in profiling. I think it would be useful to have
a perf command that runs bdiff over and over so we can find hot spots.

contrib/perf.py

@@ -25,6 +25,7 b' import random'
 import sys
 import time
 from mercurial import (
+    bdiff,
     changegroup,
     cmdutil,
     commands,
@@ -746,6 +747,30 b' def perffncacheencode(ui, repo, **opts):'
     timer(d)
     fm.end()
 
+@command('perfbdiff', revlogopts + formatteropts, '-c|-m|FILE REV')
+def perfbdiff(ui, repo, file_, rev=None, **opts):
+    """benchmark a bdiff between a revision and its delta parent"""
+    if opts.get('changelog') or opts.get('manifest'):
+        file_, rev = None, file_
+    elif rev is None:
+        raise error.CommandError('perfbdiff', 'invalid arguments')
+
+    r = cmdutil.openrevlog(repo, 'perfbdiff', file_, opts)
+
+    node = r.lookup(rev)
+    rev = r.rev(node)
+    dp = r.deltaparent(rev)
+
+    text1 = r.revision(dp)
+    text2 = r.revision(node)
+
+    def d():
+        bdiff.bdiff(text1, text2)
+
+    timer, fm = gettimer(ui, opts)
+    timer(d)
+    fm.end()
+
 @command('perfdiffwd', formatteropts)
 def perfdiffwd(ui, repo, **opts):
     """Profile diff of working directory changes"""

tests/test-contrib-perf.t

@@ -50,6 +50,7 b' perfstatus'
    perfancestorset
                  (no help text available)
    perfannotate  (no help text available)
+   perfbdiff     benchmark a bdiff between a revision and its delta parent
    perfbranchmap
                  benchmark the update of a branchmap
    perfcca       (no help text available)
@@ -112,6 +113,7 b' perfstatus'
   $ hg perfancestors
   $ hg perfancestorset 2
   $ hg perfannotate a
+  $ hg perfbdiff -c 1
   $ hg perfbranchmap
   $ hg perfcca
   $ hg perfchangegroupchangelog