dagop: just compare with the last value to deduplicate input of revancestors()

Since we're using a max heap, the current rev should be a duplicate only
if it equals to the previous one. We don't have to maintain the whole seen
set.

  # reverse(ancestors(tip)) using hg repo
  0) 0.086420
  1) 0.081051

mercurial/dagop.py

@@ -37,15 +37,15 b' def _genrevancestors(repo, revs, followf'
     if inputrev is not None:
         heapq.heappush(pendingheap, -inputrev)
 
-    seen = set()
+    lastrev = None
     while pendingheap:
         currev = -heapq.heappop(pendingheap)
         if currev == inputrev:
             inputrev = next(irevs, None)
             if inputrev is not None:
                 heapq.heappush(pendingheap, -inputrev)
-        if currev not in seen:
-            seen.add(currev)
+        if currev != lastrev:
+            lastrev = currev
             yield currev
             try:
                 for prev in cl.parentrevs(currev)[:cut]: