Optimize FacetNomral in the axiparallel case

python/dune/perftool/ufl/visitor.py

@@ -362,6 +362,15 @@ class UFL2LoopyVisitor(ModifiedTerminalTracker):
         # The normal must be restricted to be well-defined
         assert self.restriction is not Restriction.NONE
 
+        # Optimize facet normal on axiparallel grids
+        from dune.perftool.options import get_option
+        if get_option("diagonal_transformation_matrix"):
+            index, = self.indices
+            from dune.perftool.sumfact.switch import get_facedir
+            if isinstance(index, int) and index != get_facedir(self.restriction):
+                self.indices = None
+                return 0
+
         if self.restriction == Restriction.POSITIVE:
             return Variable(self.interface.name_unit_outer_normal())
         if self.restriction == Restriction.NEGATIVE: