From 1c717588223e3aa015825863ebe45fa6ad3a809d Mon Sep 17 00:00:00 2001
From: Fabio Luporini <fabio@devitocodes.com>
Date: Sat, 15 Aug 2026 14:27:01 +0100
Subject: [PATCH] compiler: Avoid fusing Clusters with different data types

---
 devito/ir/clusters/cluster.py |  3 +++
 tests/test_dse.py             |  2 +-
 tests/test_ir.py              | 21 +++++++++++++++++++++
 tests/test_operator.py        | 10 ++++++++++
 4 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/devito/ir/clusters/cluster.py b/devito/ir/clusters/cluster.py
index c4b98ca4f9..f45fa224e6 100644
--- a/devito/ir/clusters/cluster.py
+++ b/devito/ir/clusters/cluster.py
@@ -531,6 +531,9 @@ def from_clusters(cls, *clusters):
         if not all(root.guards == c.guards for c in clusters):
             raise ValueError("Cannot build a Cluster from Clusters with "
                              "non-homogeneous guards")
+        if not all(root.dtype == c.dtype for c in clusters):
+            raise ValueError("Cannot build a Cluster from Clusters with "
+                             "non-homogeneous data types")
 
         writes = set().union(*[c.scope.writes for c in clusters])
         reads = set().union(*[c.scope.reads for c in clusters])
diff --git a/tests/test_dse.py b/tests/test_dse.py
index d9f210bd9e..47b623f0cb 100644
--- a/tests/test_dse.py
+++ b/tests/test_dse.py
@@ -2961,7 +2961,7 @@ def test_fullopt(self):
         assert np.isclose(summary0[('section0', None)].oi, 3.136, atol=0.001)
 
         assert summary1[('section0', None)].ops == 31
-        assert summary1[('section1', None)].ops == 16
+        assert summary1[('section1', None)].ops == 8
         assert summary1[('section2', None)].ops == 4
         assert np.isclose(summary1[('section0', None)].oi, 1.767, atol=0.001)
 
diff --git a/tests/test_ir.py b/tests/test_ir.py
index a805fb01cf..a672f1fa53 100644
--- a/tests/test_ir.py
+++ b/tests/test_ir.py
@@ -12,6 +12,7 @@
 from devito.ir.equations import LoweredEq
 from devito.ir.equations.algorithms import dimension_sort
 from devito.ir.iet import FindNodes, Iteration
+from devito.ir.stree import stree_build
 from devito.ir.support.basic import (
     AFFINE, IRREGULAR, REGULAR, IterationInstance, Scope, TimedAccess, Vector, mocksym0,
     mocksym1
@@ -1162,6 +1163,26 @@ def test_dimension_sort(self, expr, expected):
         assert list(dimension_sort(expr)) == eval(expected)
 
 
+class TestCluster:
+
+    def test_from_clusters_mixed_dtypes(self):
+        grid = Grid(shape=(4,))
+        x, = grid.dimensions
+
+        f = Function(name='f', grid=grid, dtype=np.float32)
+        g = Function(name='g', grid=grid, dtype=np.float64)
+
+        ispace = IterationSpace([Interval(x)])
+        clusters = (Cluster(Eq(f, 1), ispace=ispace),
+                    Cluster(Eq(g, 1), ispace=ispace))
+
+        with pytest.raises(ValueError, match="non-homogeneous data types"):
+            Cluster.from_clusters(*clusters)
+
+        stree = stree_build(clusters)
+        assert len([i for i in stree.visit() if i.is_Iteration]) == 1
+
+
 class TestClusterGroup:
 
     def test_eq_hash_include_ispace(self):
diff --git a/tests/test_operator.py b/tests/test_operator.py
index f781819f7c..32bc7c4953 100644
--- a/tests/test_operator.py
+++ b/tests/test_operator.py
@@ -1447,6 +1447,16 @@ def test_permutations_without_deps(self):
             exprs = FindNodes(Expression).visit(tree[-1])
             assert len(exprs) == 3
 
+    def test_fusion_mixed_dtypes(self):
+        grid = Grid(shape=(4, 4))
+
+        f = Function(name='f', grid=grid, dtype=np.uint16)
+        g = Function(name='g', grid=grid, dtype=np.float32)
+
+        op = Operator([Eq(f, 1), Eq(g, 1)])
+
+        assert_structure(op, ['x,y'], 'x,y')
+
     @pytest.mark.parametrize('exprs,fissioned,shared', [
         # 0) Trivial case
         (('Eq(u, 1)', 'Eq(v, u.dxl)'), '(1,x)', [0]),