compiler: Prevent fusion if dep over shm functions

Author: FabioLuporini

devito/ir/clusters/cluster.py

@@ -69,13 +69,23 @@ def from_clusters(cls, *clusters):
         """
         assert len(clusters) > 0
         root = clusters[0]
+
+        if len(clusters) == 1:
+            return root
+
         if not all(root.ispace.is_compatible(c.ispace) for c in clusters):
             raise ValueError("Cannot build a Cluster from Clusters with "
                              "incompatible IterationSpace")
         if not all(root.guards == c.guards for c in clusters):
             raise ValueError("Cannot build a Cluster from Clusters with "
                              "non-homogeneous guards")
 
+        writes = set().union(*[c.scope.writes for c in clusters])
+        reads = set().union(*[c.scope.reads for c in clusters])
+        if any(f._mem_shared for f in writes & reads):
+            raise ValueError("Cannot build a Cluster from Clusters with "
+                             "read-write conflicts on shared-memory Functions")
+
         exprs = chain(*[c.exprs for c in clusters])
         ispace = IterationSpace.union(*[c.ispace for c in clusters])
 

devito/passes/clusters/misc.py

@@ -146,16 +146,13 @@ def callback(self, cgroups, prefix):
             g = list(group)
 
             for maybe_fusible in self._apply_heuristics(g):
-                if len(maybe_fusible) == 1:
+                try:
+                    # Perform fusion
+                    processed.append(Cluster.from_clusters(*maybe_fusible))
+                except ValueError:
+                    # We end up here if, for example, some Clusters have same
+                    # iteration Dimensions but different (partial) orderings
                     processed.extend(maybe_fusible)
-                else:
-                    try:
-                        # Perform fusion
-                        processed.append(Cluster.from_clusters(*maybe_fusible))
-                    except ValueError:
-                        # We end up here if, for example, some Clusters have same
-                        # iteration Dimensions but different (partial) orderings
-                        processed.extend(maybe_fusible)
 
         # Maximize effectiveness of topo-sorting at next stage by only
         # grouping together Clusters characterized by data dependencies