Added more control to when to merge.

src/gt4py/next/program_processors/runners/dace_fieldview/transformations/map_fusion_parallel.py

@@ -8,7 +8,7 @@
 
 """Implements the parallel map fusing transformation."""
 
-from typing import Any, Union
+from typing import Any, Optional, Union
 
 import dace
 from dace import properties, transformation
@@ -29,20 +29,29 @@ class ParallelMapFusion(map_fusion_helper.MapFusionHelper):
     and are in the same scope.
 
     Args:
+        only_if_common_ancestor: Only perform fusion if both Maps share at least one
+            node as direct ancestor. This will increase the locality of the merge.
         only_inner_maps: Only match Maps that are internal, i.e. inside another Map.
         only_toplevel_maps: Only consider Maps that are at the top.
-
-    Todo:
-        Add options to restrict the surrounding further, such as common input.
     """
 
     map_entry1 = transformation.transformation.PatternNode(nodes.MapEntry)
     map_entry2 = transformation.transformation.PatternNode(nodes.MapEntry)
 
+    only_if_common_ancestor = properties.Property(
+        dtype=bool,
+        default=False,
+        allow_none=False,
+        desc="Only perform fusing if the Maps share a node as parent.",
+    )
+
     def __init__(
         self,
+        only_if_common_ancestor: Optional[bool] = None,
         **kwargs: Any,
     ) -> None:
+        if only_if_common_ancestor is not None:
+            self.only_if_common_ancestor = only_if_common_ancestor
         super().__init__(**kwargs)
 
     @classmethod
@@ -80,6 +89,13 @@ def can_be_applied(
         if not util.is_parallel(graph=graph, node1=map_entry_1, node2=map_entry_2):
             return False
 
+        # Test if they have they share a node as direct ancestor.
+        if self.only_if_common_ancestor:
+            # This assumes that there is only one access node per data container in the state.
+            ancestors_1: set[nodes.Node] = {e1.src for e1 in graph.in_edges(map_entry_1)}
+            if not any(e2.src in ancestors_1 for e2 in graph.in_edges(map_entry_2)):
+                return False
+
         return True
 
     def apply(self, graph: Union[SDFGState, SDFG], sdfg: SDFG) -> None: