Fix bug when broadcasting branches in local_useless_switch rewrite

pytensor/tensor/rewriting/basic.py

@@ -1023,18 +1023,15 @@ def local_useless_switch(fgraph, node):
 
     # if left is right -> left
     if equivalent_up_to_constant_casting(left, right):
-        if left.type.broadcastable == out_bcast:
-            out_dtype = node.outputs[0].type.dtype
-            if left.type.dtype != out_dtype:
-                left = cast(left, out_dtype)
-                copy_stack_trace(node.outputs + left, left)
-            # When not casting, the other inputs of the switch aren't needed in the traceback
-            return [left]
+        if left.type.broadcastable != out_bcast:
+            left, _ = broadcast_arrays(left, cond)
 
-        else:
-            ret = broadcast_arrays(left, cond)[0]
-            copy_stack_trace(node.outputs + left, ret)
-            return [ret]
+        out_dtype = node.outputs[0].type.dtype
+        if left.type.dtype != out_dtype:
+            left = cast(left, out_dtype)
+
+        copy_stack_trace(node.outputs + node.inputs, left)
+        return [left]
 
     # This case happens with scan.
     # Elemwise{switch}(le(shape_i{id}(X), 0), 0, shape_i{id}(X)) -> shape_i{id}(X)

tests/tensor/rewriting/test_basic.py

@@ -1089,6 +1089,25 @@ def test_broadcasting_3(self):
         assert isinstance(f.maker.fgraph.outputs[0].owner.op, Alloc)
         assert not any(node.op == pt.switch for node in f.maker.fgraph.toposort())
 
+    def test_broadcasting_different_dtype(self):
+        cond = vector("x", dtype="bool")
+        float32_branch = as_tensor(np.array([0], dtype="float32"))
+        float64_branch = as_tensor(np.array([0], dtype="float64"))
+
+        out = pt.switch(cond, float32_branch, float64_branch)
+        expected_out = pt.alloc(float64_branch, cond.shape)
+
+        rewritten_out = rewrite_graph(
+            out, include=("canonicalize", "stabilize", "specialize")
+        )
+        assert equal_computations([rewritten_out], [expected_out])
+
+        out = pt.switch(cond, float64_branch, float32_branch)
+        rewritten_out = rewrite_graph(
+            out, include=("canonicalize", "stabilize", "specialize")
+        )
+        assert equal_computations([rewritten_out], [expected_out])
+
 
 class TestLocalMergeSwitchSameCond:
     @pytest.mark.parametrize(