Disable invalid inplace logic for multiple-output Composites

pytensor/tensor/rewriting/elemwise.py

@@ -59,6 +59,14 @@ class InplaceElemwiseOptimizer(GraphRewriter):
             for n in sorted(ndim.keys()):
                 print(blanc, n, ndim[n], file=stream)
 
+    def candidate_input_idxs(self, node):
+        if isinstance(node.op.scalar_op, aes.Composite) and len(node.outputs) > 1:
+            # TODO: Implement specialized InplaceCompositeOptimizer with logic
+            #  needed to correctly assign inplace for multi-output Composites
+            return []
+        else:
+            return range(len(node.outputs))
+
     def apply(self, fgraph):
         r"""
 
@@ -149,7 +157,7 @@ class InplaceElemwiseOptimizer(GraphRewriter):
 
                 baseline = op.inplace_pattern
                 candidate_outputs = [
-                    i for i in range(len(node.outputs)) if i not in baseline
+                    i for i in self.candidate_input_idxs(node) if i not in baseline
                 ]
                 # node inputs that are Constant, already destroyed,
                 # or fgraph protected inputs and fgraph outputs can't be used as
@@ -167,7 +175,7 @@ class InplaceElemwiseOptimizer(GraphRewriter):
                 ]
             else:
                 baseline = []
-                candidate_outputs = list(range(len(node.outputs)))
+                candidate_outputs = self.candidate_input_idxs(node)
                 # node inputs that are Constant, already destroyed,
                 # fgraph protected inputs and fgraph outputs can't be used as inplace
                 # target.

tests/tensor/rewriting/test_elemwise.py

@@ -4,6 +4,7 @@ import numpy as np
 import pytest
 
 import pytensor
+from pytensor import In
 from pytensor import scalar as aes
 from pytensor import shared
 from pytensor import tensor as at
@@ -1024,6 +1025,34 @@ class TestFusion:
             np.random.random((5, 5)), np.random.random((5, 5)), np.random.random((5, 5))
         )
 
+    def test_fusion_multiout_inplace(self):
+        x = vector("x")
+
+        # Create Composite where inplacing the first non-constant output would corrupt the second output
+        xs = aes.float64("xs")
+        outs = (
+            Elemwise(Composite([xs], [xs + 1, aes.cos(xs + 1) + xs]))
+            .make_node(x)
+            .outputs
+        )
+
+        f = pytensor.function(
+            [In(x, mutable=True)],
+            outs,
+            mode=self.mode.including("inplace"),
+        )
+        (composite_node,) = f.maker.fgraph.apply_nodes
+
+        # Destroy map must be None or the last toposorted output
+        destroy_map = composite_node.op.destroy_map
+        assert (destroy_map == {}) or (
+            destroy_map == {1: [composite_node.inputs.index(x)]}
+        )
+
+        res = f([0, 1, 2])
+        assert np.allclose(res[0], [1, 2, 3])
+        assert np.allclose(res[1], np.cos([1, 2, 3]) + np.array([0, 1, 2]))
+
     @pytest.mark.skipif(not config.cxx, reason="No cxx compiler")
     def test_no_c_code(self):
         r"""Make sure we avoid fusions for `Op`\s without C code implementations."""