Fix vectorize_graph bug when replacements were provided only some o…

…utputs of a node

The provided output could be silently ignored and replaced by the new output of the vectorized node.

The changes also avoid vectorizing multiple-output nodes when none of the unreplaced outputs are needed.

pytensor/graph/basic.py

@@ -1439,15 +1439,16 @@ def io_toposort(
         order = []
         while todo:
             cur = todo.pop()
-            # We suppose that all outputs are always computed
-            if cur.outputs[0] in computed:
+            if all(out in computed for out in cur.outputs):
                 continue
             if all(i in computed or i.owner is None for i in cur.inputs):
                 computed.update(cur.outputs)
                 order.append(cur)
             else:
                 todo.append(cur)
-                todo.extend(i.owner for i in cur.inputs if i.owner)
+                todo.extend(
+                    i.owner for i in cur.inputs if (i.owner and i not in computed)
+                )
         return order
 
     compute_deps = None

pytensor/graph/replace.py

@@ -306,6 +306,11 @@ def vectorize_graph(
         vect_inputs = [vect_vars.get(inp, inp) for inp in node.inputs]
         vect_node = vectorize_node(node, *vect_inputs)
         for output, vect_output in zip(node.outputs, vect_node.outputs):
+            if output in vect_vars:
+                # This can happen when some outputs of a multi-output node are given a replacement,
+                # while some of the remaining outputs are still needed in the graph.
+                # We make sure we don't overwrite the provided replacement with the newly vectorized output
+                continue
             vect_vars[output] = vect_output
 
     seq_vect_outputs = [vect_vars[out] for out in seq_outputs]

tests/graph/test_basic.py

@@ -34,7 +34,7 @@
 from pytensor.tensor.type import TensorType, iscalars, matrix, scalars, vector
 from pytensor.tensor.type_other import NoneConst
 from pytensor.tensor.variable import TensorVariable
-from tests.graph.utils import MyInnerGraphOp
+from tests.graph.utils import MyInnerGraphOp, op_multiple_outputs
 
 
 class MyType(Type):
@@ -287,6 +287,45 @@ def test_outputs_clients(self):
         all = io_toposort([], o0.outputs)
         assert all == [o0]
 
+    def test_multi_output_nodes(self):
+        l0, r0 = op_multiple_outputs(shared(0.0))
+        l1, r1 = op_multiple_outputs(shared(0.0))
+
+        v0 = r0 + 1
+        v1 = pt.exp(v0)
+        out = r1 * v1
+
+        # When either r0 or r1 is provided as an input, the respective node shouldn't be part of the toposort
+        assert set(io_toposort([], [out])) == {
+            r0.owner,
+            r1.owner,
+            v0.owner,
+            v1.owner,
+            out.owner,
+        }
+        assert set(io_toposort([r0], [out])) == {
+            r1.owner,
+            v0.owner,
+            v1.owner,
+            out.owner,
+        }
+        assert set(io_toposort([r1], [out])) == {
+            r0.owner,
+            v0.owner,
+            v1.owner,
+            out.owner,
+        }
+        assert set(io_toposort([r0, r1], [out])) == {v0.owner, v1.owner, out.owner}
+
+        # When l0 and/or l1 are provided, we still need to compute the respective nodes
+        assert set(io_toposort([l0, l1], [out])) == {
+            r0.owner,
+            r1.owner,
+            v0.owner,
+            v1.owner,
+            out.owner,
+        }
+
 
 class TestEval:
     def setup_method(self):

tests/graph/test_replace.py

@@ -5,10 +5,15 @@
 import pytensor.tensor as pt
 from pytensor import config, function, shared
 from pytensor.graph.basic import equal_computations, graph_inputs
-from pytensor.graph.replace import clone_replace, graph_replace, vectorize_graph
+from pytensor.graph.replace import (
+    clone_replace,
+    graph_replace,
+    vectorize_graph,
+    vectorize_node,
+)
 from pytensor.tensor import dvector, fvector, vector
 from tests import unittest_tools as utt
-from tests.graph.utils import MyOp, MyVariable
+from tests.graph.utils import MyOp, MyVariable, op_multiple_outputs
 
 
 class TestCloneReplace:
@@ -227,8 +232,6 @@ def test_graph_replace_disconnected(self):
 
 
 class TestVectorizeGraph:
-    # TODO: Add tests with multiple outputs, constants, and other singleton types
-
     def test_basic(self):
         x = pt.vector("x")
         y = pt.exp(x) / pt.sum(pt.exp(x))
@@ -260,3 +263,63 @@ def test_multiple_outputs(self):
         new_y1_res, new_y2_res = fn(new_x_test)
         np.testing.assert_allclose(new_y1_res, [0, 3, 6])
         np.testing.assert_allclose(new_y2_res, [2, 5, 8])
+
+    def test_multi_output_node(self):
+        x = pt.scalar("x")
+        node = op_multiple_outputs.make_node(x)
+        y1, y2 = node.outputs
+        out = pt.add(y1, y2)
+
+        new_x = pt.vector("new_x")
+        new_y1 = pt.vector("new_y1")
+        new_y2 = pt.vector("new_y2")
+
+        # Cases where either x or both of y1 and y2 are given replacements
+        new_out = vectorize_graph(out, {x: new_x})
+        expected_new_out = pt.add(*vectorize_node(node, new_x).outputs)
+        assert equal_computations([new_out], [expected_new_out])
+
+        new_out = vectorize_graph(out, {y1: new_y1, y2: new_y2})
+        expected_new_out = pt.add(new_y1, new_y2)
+        assert equal_computations([new_out], [expected_new_out])
+
+        new_out = vectorize_graph(out, {x: new_x, y1: new_y1, y2: new_y2})
+        expected_new_out = pt.add(new_y1, new_y2)
+        assert equal_computations([new_out], [expected_new_out])
+
+        # Special case where x is given a replacement as well as only one of y1 and y2
+        # The graph combines the replaced variable with the other vectorized output
+        new_out = vectorize_graph(out, {x: new_x, y1: new_y1})
+        expected_new_out = pt.add(new_y1, vectorize_node(node, new_x).outputs[1])
+        assert equal_computations([new_out], [expected_new_out])
+
+    def test_multi_output_node_random_variable(self):
+        """This is a regression test for #569.
+
+        Functionally, it covers the same case as `test_multiple_output_node`
+        """
+
+        # RandomVariables have two outputs, a hidden RNG and the visible draws
+        beta0 = pt.random.normal(name="beta0")
+        beta1 = pt.random.normal(name="beta1")
+
+        out1 = beta0 + 1
+        out2 = beta1 * pt.exp(out1)
+
+        # We replace the second output of each RandomVariable
+        new_beta0 = pt.tensor("new_beta0", shape=(3,))
+        new_beta1 = pt.tensor("new_beta1", shape=(3,))
+
+        new_outs = vectorize_graph(
+            [out1, out2],
+            replace={
+                beta0: new_beta0,
+                beta1: new_beta1,
+            },
+        )
+
+        expected_new_outs = [
+            new_beta0 + 1,
+            new_beta1 * pt.exp(new_beta0 + 1),
+        ]
+        assert equal_computations(new_outs, expected_new_outs)