--- a/hgext3rd/evolve/stablerange.py	Thu Mar 23 12:53:39 2017 +0100
+++ b/hgext3rd/evolve/stablerange.py	Fri Mar 24 05:15:25 2017 +0100
@@ -174,6 +174,8 @@
         # the revision computed anyway, and passing that knowledge around might
         # help to slice one of its subranges also containings a merge.
         self._revsinrangecache = {}
+        # caching parent call # as we do so many of them
+        self._parentscache = {}
 
     def warmup(self, repo, heads):
         """warm the cache up to 'heads'"""
@@ -194,7 +196,7 @@
             if revdepth is not None:
                 stack.pop()
                 continue
-            p1, p2 = cl.parentrevs(current)
+            p1, p2 = self._parents(current, cl.parentrevs)
             if p1 == nullrev:
                 # root case
                 revdepth = 1
@@ -249,6 +251,13 @@
         assert len(revs) == self.rangelength(repo, rangeid)
         return revs
 
+    def _parents(self, rev, func):
+        parents = self._parentscache.get(rev)
+        if parents is None:
+            parents = func(rev)
+            self._parentscache[rev] = parents
+        return parents
+
     @staticmethod
     def _depthmerge(cl, rev, p1, p2, stack, cache):
         # sub method to simplify the main 'depthrev' one
@@ -319,7 +328,7 @@
         This function also have the important task to update the revscache of
         the parent revs if possible and needed"""
         # is this is a merge, there is not need to prepare the parents.
-        p1, p2 = repo.changelog.parentrevs(rangeid[0])
+        p1, p2 = self._parents(rangeid[0], repo.changelog.parentrevs)
         if p2 != nodemod.nullrev:
             return None
         parentrange = (p1, rangeid[1])
@@ -354,7 +363,7 @@
         return slicepoint
 
     def _slicesrangeat(self, repo, rangeid, globalindex):
-        p1, p2 = repo.changelog.parentrevs(rangeid[0])
+        p1, p2 = self._parents(rangeid[0], repo.changelog.parentrevs)
         if p2 != nodemod.nullrev:
             return self._slicesrangeatmerge(repo, rangeid, globalindex)
         assert p1 != nodemod.nullrev
@@ -402,9 +411,10 @@
         else:
             bheads = set(bottomrevs)
             parentrevs = cl.parentrevs
+            parents = self._parents
             du = bheads.difference_update
             for r in bottomrevs:
-                du(parentrevs(r))
+                du(parents(r, parentrevs))
             # if len(bheads) == 1:
             #     assert 1 == len(repo.revs('roots(%ld)', top._revs))
         if len(bheads) == 1: