perf: add function for obtaining manifest revision

This will use the modern API if available or fall back to the
legacy direct revlog access case. Without this, the perf command
won't work on all code bases.

Differential Revision: https://phab.mercurial-scm.org/D4391

contrib/perf.py

@@ -1127,6 +1127,16 b' def _bdiffworker(q, blocks, xdiff, ready'
         with ready:
             ready.wait()
 
+def _manifestrevision(repo, mnode):
+    ml = repo.manifestlog
+
+    if util.safehasattr(ml, 'getstorage'):
+        store = ml.getstorage(b'')
+    else:
+        store = ml._revlog
+
+    return store.revision(mnode)
+
 @command('perfbdiff', revlogopts + formatteropts + [
     ('', 'count', 1, 'number of revisions to test (when using --startrev)'),
     ('', 'alldata', False, 'test bdiffs for all associated revisions'),
@@ -1172,9 +1182,9 b' def perfbdiff(ui, repo, file_, rev=None,'
         if opts['alldata']:
             # Load revisions associated with changeset.
             ctx = repo[rev]
-            mtext = repo.manifestlog._revlog.revision(ctx.manifestnode())
+            mtext = _manifestrevision(repo, ctx.manifestnode())
             for pctx in ctx.parents():
-                pman = repo.manifestlog._revlog.revision(pctx.manifestnode())
+                pman = _manifestrevision(repo, pctx.manifestnode())
                 textpairs.append((pman, mtext))
 
             # Load filelog revisions by iterating manifest delta.
@@ -1264,9 +1274,9 b' def perfunidiff(ui, repo, file_, rev=Non'
         if opts['alldata']:
             # Load revisions associated with changeset.
             ctx = repo[rev]
-            mtext = repo.manifestlog._revlog.revision(ctx.manifestnode())
+            mtext = _manifestrevision(repo, ctx.manifestnode())
             for pctx in ctx.parents():
-                pman = repo.manifestlog._revlog.revision(pctx.manifestnode())
+                pman = _manifestrevision(repo, pctx.manifestnode())
                 textpairs.append((pman, mtext))
 
             # Load filelog revisions by iterating manifest delta.