Fix bug in local_div_switch_sink rewrite

pytensor/graph/basic.py

@@ -622,9 +622,9 @@ def convert_string_keys_to_variables(inputs_to_values) -> dict["Variable", Any]:
                 if isinstance(key, str):
                     matching_vars = get_var_by_name([self], key)
                     if not matching_vars:
-                        raise Exception(f"{key} not found in graph")
+                        raise ValueError(f"{key} not found in graph")
                     elif len(matching_vars) > 1:
-                        raise Exception(f"Found multiple variables with name {key}")
+                        raise ValueError(f"Found multiple variables with name {key}")
                     new_input_to_values[matching_vars[0]] = value
                 else:
                     new_input_to_values[key] = value

pytensor/tensor/rewriting/math.py

@@ -699,7 +699,10 @@ def local_div_switch_sink(fgraph, node):
             # will point to the new division op.
             copy_stack_trace(node.outputs, fdiv)
 
-            fct = switch(switch_cond, zero_switch_input, fdiv)
+            if branch == 0:
+                fct = switch(switch_cond, zero_switch_input, fdiv)
+            else:
+                fct = switch(switch_cond, fdiv, zero_switch_input)
 
             # Tell debug_mode than the output is correct, even if nan disappear
             fct.tag.values_eq_approx = values_eq_approx_remove_nan

tests/tensor/rewriting/test_math.py

@@ -2163,7 +2163,7 @@ def test_local_mul_div_switch_sink_cast(self, op, rewrite):
         # The zero branch upcasts the output, so we can't ignore its dtype
         zero_branch = constant(np.array(0, dtype="float64"), name="zero_branch")
         other_branch = scalar("other_branch", dtype="float32")
-        outer_var = scalar("mul_var", dtype="bool")
+        outer_var = scalar("outer_var", dtype="bool")
 
         out = op(switch(cond, zero_branch, other_branch), outer_var)
         fgraph = FunctionGraph(outputs=[out], clone=False)
@@ -2173,6 +2173,27 @@ def test_local_mul_div_switch_sink_cast(self, op, rewrite):
         expected_out = switch(cond, zero_branch, op(other_branch, outer_var))
         assert equal_computations([new_out], [expected_out])
 
+    @pytest.mark.parametrize(
+        "op, rewrite", [(mul, local_mul_switch_sink), (true_div, local_div_switch_sink)]
+    )
+    def test_local_mul_div_switch_sink_branch_order(self, op, rewrite):
+        cond = scalar("cond", dtype="bool")
+        zero_branch = constant(np.array(0.0, dtype="float64"), "zero_branch")
+        other_branch = scalar("other_branch", dtype="float64")
+        outer_var = scalar("outer_var", dtype="float64")
+
+        left = op(switch(cond, zero_branch, other_branch), outer_var)
+        right = op(switch(cond, other_branch, zero_branch), outer_var)
+        fgraph = FunctionGraph(outputs=[left, right], clone=False)
+        [new_left] = rewrite.transform(fgraph, left.owner)
+        [new_right] = rewrite.transform(fgraph, right.owner)
+
+        expected_left = switch(cond, zero_branch, op(other_branch, outer_var))
+        expected_right = switch(cond, op(other_branch, outer_var), zero_branch)
+        assert equal_computations(
+            [new_left, new_right], [expected_left, expected_right]
+        )
+
 
 @pytest.mark.skipif(
     config.cxx == "",