fix sim scheduler for circuits with POs that are also used internally

tests/test_logic_sim.py

@@ -20,6 +20,18 @@ def test_dangling():
     sim.simulate(p)
     assert p[1,0] == logic.ONE
 
+def test_used_output():
+    c = bench.parse('input(i0) output(o0) output(o1) o0=BUF1(i0) o1=BUF(o0)')
+    sim = LogicSim2V(c)
+    expect = mvarray('000', '111')
+    actual = sim.simulate(expect.copy())
+    np.testing.assert_array_equal(
+        expect[c.io_locs('o0')],
+        actual[c.io_locs('o0')])
+    np.testing.assert_array_equal(
+        expect[c.io_locs('o1')],
+        actual[c.io_locs('o1')])
+
 def assert_equal_shape_and_contents(actual, desired):
     desired = np.array(desired, dtype=np.uint8)
     assert actual.shape == desired.shape