tests: Add an additional test for loop scheduling

tests/test_operator.py

@@ -1444,6 +1444,42 @@ def test_fission_for_parallelism(self, exprs, fissioned, shared):
             # Fission happened
             assert i[exp_depth].dim is exp_dim
 
+    def test_fission_for_parallelism_b(self):
+        so = 2
+        grid = Grid(shape=(10, 10, 10))
+        x, y, z = grid.dimensions
+
+        f0 = TimeFunction(name='f0', grid=grid, space_order=so, staggered=(x,))
+        f1 = TimeFunction(name='f1', grid=grid, space_order=so, staggered=(y,))
+
+        f2 = TimeFunction(name='f2', grid=grid, space_order=so, staggered=(x, z))
+        f3 = TimeFunction(name='f3', grid=grid, space_order=so, staggered=(y, z))
+
+        f4 = TimeFunction(name='f4', grid=grid, space_order=so, staggered=NODE)
+
+        eq0 = Eq(f2, f0.dz)
+        eq1 = Eq(f3, f1.dz)
+        eq2 = Eq(f4, f2 + f3)
+
+        op = Operator([eq0, eq1, eq2])
+
+        trees = retrieve_iteration_tree(op)
+
+        # First two equations should be fused for parallelism, but the third should be
+        # fissioned
+        assert len(trees) == 2
+        assert len(trees[0][-1].nodes[0].exprs) == 2
+        assert len(trees[1][-1].nodes[0].exprs) == 1
+
+        def check_expr_contents(expr, expected):
+            assert all(f.base in expr.expr_symbols for f in expected)
+
+        # Check expressions match equations
+        check_expr_contents(trees[0][-1].nodes[0].exprs[0], (f2, f0))
+        check_expr_contents(trees[0][-1].nodes[0].exprs[1], (f3, f1))
+
+        check_expr_contents(trees[1][-1].nodes[0].exprs[0], (f4, f2, f3))
+
     @pytest.mark.parametrize('exprs', [
         # 0) Storage related dependence
         ('Eq(u.forward, v)', 'Eq(v, u.dxl)'),