dirstate: narrow gathering of parent data

The parent data are only going to be useful is the file might be clean. And it
might only be clean if it is tracked in both p1 and the working copy.

Differential Revision: https://phab.mercurial-scm.org/D11584

mercurial/dirstate.py

@@ -525,11 +525,8 b' class dirstate(object):'
             if entry is not None and entry.added:
                 return  # avoid dropping copy information (maybe?)
 
-        # this mean we are doing call for file we do not really care about the
-        # data (eg: added or removed), however this should be a minor overhead
-        # compared to the overall update process calling this.
         parentfiledata = None
-        if wc_tracked:
+        if wc_tracked and p1_tracked:
             parentfiledata = self._get_filedata(filename)
 
         self._map.reset_state(