compiler: Pull some aspects of DAG construction out and cache

Author: EdCaunt

devito/ir/support/basic.py

@@ -834,6 +834,10 @@ def __init__(self, exprs, rules=None):
         self.rules = as_tuple(rules)
         assert all(callable(i) for i in self.rules)
 
+    @cached_property
+    def thingy(self):
+        return any(i.cause for i in self.d_anti_gen())
+
     @memoized_generator
     def writes_gen(self):
         """

devito/passes/clusters/misc.py

@@ -362,7 +362,9 @@ def is_cross(source, sink):
                 # (intuitively, "the loop nests are to be kept separated")
                 # * All ClusterGroups between `cg0` and `cg1` must precede `cg1`
                 # * All ClusterGroups after `cg1` cannot precede `cg1`
-                if any(i.cause & prefix for i in scope.d_anti_gen()):
+                # FIXME: Attach to the scope
+                # if any(i.cause & prefix for i in scope.d_anti_gen()):
+                if prefix and scope.thingy:
                     for cg2 in cgroups[n:cgroups.index(cg1)]:
                         dag.add_edge(cg2, cg1)
                     for cg2 in cgroups[cgroups.index(cg1)+1:]: