diff -r a7c0c5b5a50f -r 845e5b313783 mercurial/pure/parsers.py
--- a/mercurial/pure/parsers.py	Wed Nov 06 14:13:19 2019 +0100
+++ b/mercurial/pure/parsers.py	Wed Nov 06 14:13:19 2019 +0100
@@ -10,8 +10,12 @@
 import struct
 import zlib
 
-from ..node import nullid
-from .. import pycompat
+from ..node import nullid, nullrev
+from .. import (
+    pycompat,
+    revlogutils,
+    util,
+)
 
 stringio = pycompat.bytesio
 
@@ -43,6 +47,17 @@
 
 
 class BaseIndexObject(object):
+    @util.propertycache
+    def nodemap(self):
+        nodemap = revlogutils.NodeMap({nullid: nullrev})
+        for r in range(0, len(self)):
+            n = self[r][7]
+            nodemap[n] = r
+        return nodemap
+
+    def clearcaches(self):
+        self.__dict__.pop('nodemap', None)
+
     def __len__(self):
         return self._lgt + len(self._extra)