diff --git a/mercurial/graphmod.py b/mercurial/graphmod.py
--- a/mercurial/graphmod.py
+++ b/mercurial/graphmod.py
@@ -110,79 +110,81 @@ def groupbranchiter(revs, parentsfunc):
     # parts of the initial set should be emitted.
     groups = [([], unblocked)]
     for current in revs:
-        # Look for a subgroup blocked, waiting for the current revision.
-        matching = [i for i, g in enumerate(groups) if current in g[1]]
+        if True:
+            # Seek for a subgroup blocked, waiting for the current revision.
+            matching = [i for i, g in enumerate(groups) if current in g[1]]
 
-        if matching:
-            # The main idea is to gather together all sets that await on the
-            # same revision.
-            #
-            # This merging is done at the time we are about to add this common
-            # awaited to the subgroup for simplicity purpose. Such merge could
-            # happen sooner when we update the "blocked" set of revision.
-            #
-            # We also always keep the oldest subgroup first. We can probably
-            # improve the behavior by having the longuest set first. That way,
-            # graph algorythms could minimise the length of parallele lines
-            # their draw. This is currently not done.
-            targetidx = matching.pop(0)
-            trevs, tparents = groups[targetidx]
-            for i in matching:
-                gr = groups[i]
-                trevs.extend(gr[0])
-                tparents |= gr[1]
-            # delete all merged subgroups (but the one we keep)
-            # (starting from the last subgroup for performance and sanity reason)
-            for i in reversed(matching):
-                del groups[i]
-        else:
-            # This is a new head. We create a new subgroup for it.
-            targetidx = len(groups)
-            groups.append(([], set([current])))
+            if matching:
+                # The main idea is to gather together all sets that await on
+                # the same revision.
+                #
+                # This merging is done at the time we are about to add this
+                # common awaited to the subgroup for simplicity purpose. Such
+                # merge could happen sooner when we update the "blocked" set of
+                # revision.
+                #
+                # We also always keep the oldest subgroup first. We can
+                # probably improve the behavior by having the longuest set
+                # first. That way, graph algorythms could minimise the length
+                # of parallele lines their draw. This is currently not done.
+                targetidx = matching.pop(0)
+                trevs, tparents = groups[targetidx]
+                for i in matching:
+                    gr = groups[i]
+                    trevs.extend(gr[0])
+                    tparents |= gr[1]
+                # delete all merged subgroups (but the one we keep) (starting
+                # from the last subgroup for performance and sanity reason)
+                for i in reversed(matching):
+                    del groups[i]
+            else:
+                # This is a new head. We create a new subgroup for it.
+                targetidx = len(groups)
+                groups.append(([], set([current])))
 
-        gr = groups[targetidx]
+            gr = groups[targetidx]
 
-        # We now adds the current nodes to this subgroups. This is done after
-        # the subgroup merging because all elements from a subgroup that relied
-        # on this rev must preceed it.
-        #
-        # we also update the <parents> set to includes the parents on the
-        # new nodes.
-        gr[0].append(current)
-        gr[1].remove(current)
-        gr[1].update([p for p in parentsfunc(current) if p > nullrev])
+            # We now adds the current nodes to this subgroups. This is done
+            # after the subgroup merging because all elements from a subgroup
+            # that relied on this rev must preceed it.
+            #
+            # we also update the <parents> set to includes the parents on the
+            # new nodes.
+            gr[0].append(current)
+            gr[1].remove(current)
+            gr[1].update([p for p in parentsfunc(current) if p > nullrev])
 
-        # Look for a subgroup to display
-        #
-        # When unblocked is empty (if clause), We are not waiting over any
-        # revision during the first iteration (if no priority was given) or if
-        # we outputed a whole disconnected sets of the graph (reached a root).
-        # In that case we arbitrarily takes the oldest known subgroup. The
-        # heuristique could probably be better.
-        #
-        # Otherwise (elif clause) this mean we have some emitted revision.  if
-        # the subgroup awaits on the same revision that the outputed ones, we
-        # can safely output it.
-        if not unblocked:
-            if len(groups) > 1:  # display other subset
-                targetidx = 1
-                gr = groups[1]
-        elif not gr[1] & unblocked:
-            gr = None
+            # Look for a subgroup to display
+            #
+            # When unblocked is empty (if clause), We are not waiting over any
+            # revision during the first iteration (if no priority was given) or
+            # if we outputed a whole disconnected sets of the graph (reached a
+            # root).  In that case we arbitrarily takes the oldest known
+            # subgroup. The heuristique could probably be better.
+            #
+            # Otherwise (elif clause) this mean we have some emitted revision.
+            # if the subgroup awaits on the same revision that the outputed
+            # ones, we can safely output it.
+            if not unblocked:
+                if len(groups) > 1:  # display other subset
+                    targetidx = 1
+                    gr = groups[1]
+            elif not gr[1] & unblocked:
+                gr = None
 
-        if gr is not None:
-            # update the set of awaited revisions with the one from the
-            # subgroup
-            unblocked |= gr[1]
-            # output all revisions in the subgroup
-            for r in gr[0]:
-                yield r
-            # delete the subgroup that you just output
-            # unless it is groups[0] in which case you just empty it.
-            if targetidx:
-                del groups[targetidx]
-            else:
-                gr[0][:] = []
+            if gr is not None:
+                # update the set of awaited revisions with the one from the
+                # subgroup
+                unblocked |= gr[1]
+                # output all revisions in the subgroup
+                for r in gr[0]:
+                    yield r
+                # delete the subgroup that you just output
+                # unless it is groups[0] in which case you just empty it.
+                if targetidx:
+                    del groups[targetidx]
+                else:
+                    gr[0][:] = []
 
 def dagwalker(repo, revs):
     """cset DAG generator yielding (id, CHANGESET, ctx, [parentids]) tuples