revlogdeltas: pass revision number to _candidatesgroups

The `_candidates_groups` logic works on revisions, so the nodes are currently
just converted to revs at the top of the function. It seems cleaner to instead
pass revision numbers to the function.

Having this conversion out of the way will help for further cleanups.

mercurial/revlogutils/deltas.py

@@ -576,7 +576,6 b' def _candidategroups(revlog, p1, p2, cac'
     gdelta = revlog._generaldelta
     curr = len(revlog)
     prev = curr - 1
-    p1r, p2r = revlog.rev(p1), revlog.rev(p2)
 
     # should we try to build a delta?
     if prev != nullrev and revlog._storedeltachains:
@@ -593,7 +592,7 b' def _candidategroups(revlog, p1, p2, cac'
 
         if gdelta:
             # exclude already lazy tested base if any
-            parents = [p for p in (p1r, p2r)
+            parents = [p for p in (p1, p2)
                        if p != nullrev and p not in tested]
 
             if not revlog._deltabothparents and len(parents) == 2:
@@ -734,7 +733,8 b' class deltacomputer(object):'
 
         deltainfo = None
         deltas_limit = revinfo.textlen * LIMIT_DELTA2TEXT
-        groups = _candidategroups(self.revlog, p1, p2, cachedelta)
+        p1r, p2r = revlog.rev(p1), revlog.rev(p2)
+        groups = _candidategroups(self.revlog, p1r, p2r, cachedelta)
         for candidaterevs in groups:
             # filter out delta base that will never produce good delta
             candidaterevs = [r for r in candidaterevs