diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -2808,6 +2808,11 @@
         fparent1 = manifest1.get(fname, nullid)
         fparent2 = manifest2.get(fname, nullid)
         if isinstance(fctx, context.filectx):
+            # This block fast path most comparison, making the assumption that
+            # is a bare filectx is used, no merge happened on this file., and
+            # therefor they are chance of needing to a create a new file
+            # revision, even if the content was identical to one of the
+            # parents.
             node = fctx.filenode()
             if node in [fparent1, fparent2]:
                 self.ui.debug(b'reusing %s filelog entry\n' % fname)