compiler: Tweak lowering of HaloTouch

devito/ir/stree/algorithms.py

@@ -18,7 +18,7 @@ def stree_build(clusters, profiler=None, **kwargs):
     """
     Create a ScheduleTree from a ClusterGroup.
     """
-    clusters = preprocess(clusters)
+    clusters = preprocess(clusters, **kwargs)
 
     stree = ScheduleTree()
     section = None
@@ -130,7 +130,7 @@ def stree_build(clusters, profiler=None, **kwargs):
 base = IterationInterval(Interval(None), [], Any)
 
 
-def preprocess(clusters):
+def preprocess(clusters, options=None, **kwargs):
     """
     Remove the HaloTouch's from `clusters` and create a mapping associating
     each removed HaloTouch to the first Cluster necessitating it.
@@ -146,7 +146,8 @@ def preprocess(clusters):
 
             found = []
             for c1 in list(queue):
-                if c1.halo_scheme.distributed_aindices & dims:
+                if c1.guards == c.guards and \
+                   c1.halo_scheme.distributed_aindices & dims:
                     found.append(c1)
                     queue.remove(c1)
 
@@ -155,6 +156,13 @@ def preprocess(clusters):
 
             processed.append(c.rebuild(syncs=syncs, halo_scheme=halo_scheme))
 
+    # Sanity check!
+    try:
+        assert not queue
+    except AssertionError:
+        if options['mpi']:
+            raise RuntimeError("Unsupported MPI for the given equations")
+
     return processed