compiler: Drop redundant code

devito/ir/iet/visitors.py

@@ -873,7 +873,6 @@ def default_retval(cls):
         the nodes of type ``child_types`` retrieved by the search. This behaviour
         can be changed through this parameter. Accepted values are:
         - 'immediate': only the closest matching ancestor is mapped.
-        - 'groupby': the matching ancestors are grouped together as a single key.
     """
 
     def __init__(self, parent_type=None, child_types=None, mode=None):
@@ -886,7 +885,7 @@ def __init__(self, parent_type=None, child_types=None, mode=None):
             assert issubclass(parent_type, Node)
             self.parent_type = parent_type
         self.child_types = as_tuple(child_types) or (Call, Expression)
-        assert mode in (None, 'immediate', 'groupby')
+        assert mode in (None, 'immediate')
         self.mode = mode
 
     def visit_object(self, o, ret=None, **kwargs):
@@ -903,9 +902,7 @@ def visit_Node(self, o, ret=None, parents=None, in_parent=False):
         if parents is None:
             parents = []
         if isinstance(o, self.child_types):
-            if self.mode == 'groupby':
-                ret.setdefault(as_tuple(parents), []).append(o)
-            elif self.mode == 'immediate':
+            if self.mode == 'immediate':
                 if in_parent:
                     ret.setdefault(parents[-1], []).append(o)
                 else:

devito/passes/iet/mpi.py

@@ -83,15 +83,7 @@ def _hoist_invariant(iet):
     hsmapper = {}
     imapper = defaultdict(list)
 
-    iter_mapper = MapNodes(Iteration, HaloSpot, 'immediate').visit(iet)
-
-    # Drop void `halo_scheme`s from the analysis
-    iter_mapper = {k: [hs for hs in v if not hs.halo_scheme.is_void]
-                   for k, v in iter_mapper.items()}
-
-    iter_mapper = {k: v for k, v in iter_mapper.items() if k is not None}
-
-    iter_mapper = {k: v for k, v in iter_mapper.items() if len(v) > 1}
+    iter_mapper = filter_iter_mapper(iet)
 
     for it, halo_spots in iter_mapper.items():
         for hs0, hs1 in combinations(halo_spots, r=2):
@@ -168,11 +160,7 @@ def _merge_halospots(iet):
 
     mapper = {}
 
-    iter_mapper = MapNodes(Iteration, HaloSpot, 'immediate').visit(iet)
-
-    iter_mapper = {k: v for k, v in iter_mapper.items() if k is not None}
-
-    iter_mapper = {k: v for k, v in iter_mapper.items() if len(v) > 1}
+    iter_mapper = filter_iter_mapper(iet)
 
     for it, halo_spots in iter_mapper.items():
         scope = Scope([e.expr for e in FindNodes(Expression).visit(it)])
@@ -366,6 +354,20 @@ def mpiize(graph, **kwargs):
 
 # *** Utilities
 
+def filter_iter_mapper(iet):
+    """
+    Given an IET, return a mapper from Iterations to the HaloSpots.
+    Additionally, filter out Iterations that are not of interest.
+    """
+    iter_mapper = MapNodes(Iteration, HaloSpot, 'immediate').visit(iet)
+    iter_mapper = {k: [hs for hs in v if not hs.halo_scheme.is_void]
+                   for k, v in iter_mapper.items()}
+    iter_mapper = {k: v for k, v in iter_mapper.items() if k is not None}
+    iter_mapper = {k: v for k, v in iter_mapper.items() if len(v) > 1}
+
+    return iter_mapper
+
+
 def _make_cond_mapper(iet):
     cond_mapper = MapHaloSpots().visit(iet)
     return {hs: {i for i in v if i.is_Conditional and