Only apply MCMT plugin on MCMTGate (#13596)

* Only apply MCMT plugin on MCMTGate

* add checks for other gates

* fix reno

* use == instead of equiv

qiskit/transpiler/passes/synthesis/hls_plugins.py

@@ -420,12 +420,13 @@
     C3XGate,
     C4XGate,
     PauliEvolutionGate,
+    PermutationGate,
+    MCMTGate,
     ModularAdderGate,
     HalfAdderGate,
     FullAdderGate,
     MultiplierGate,
 )
-from qiskit.transpiler.exceptions import TranspilerError
 from qiskit.transpiler.coupling import CouplingMap
 
 from qiskit.synthesis.clifford import (
@@ -467,6 +468,7 @@
     multiplier_qft_r17,
     multiplier_cumulative_h18,
 )
+from qiskit.quantum_info.operators import Clifford
 from qiskit.transpiler.passes.routing.algorithms import ApproximateTokenSwapper
 from .plugin import HighLevelSynthesisPlugin
 
@@ -484,6 +486,9 @@ class DefaultSynthesisClifford(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Clifford."""
+        if not isinstance(high_level_object, Clifford):
+            return None
+
         decomposition = synth_clifford_full(high_level_object)
         return decomposition
 
@@ -497,6 +502,9 @@ class AGSynthesisClifford(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Clifford."""
+        if not isinstance(high_level_object, Clifford):
+            return None
+
         decomposition = synth_clifford_ag(high_level_object)
         return decomposition
 
@@ -513,10 +521,14 @@ class BMSynthesisClifford(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Clifford."""
+        if not isinstance(high_level_object, Clifford):
+            return None
+
         if high_level_object.num_qubits <= 3:
             decomposition = synth_clifford_bm(high_level_object)
         else:
             decomposition = None
+
         return decomposition
 
 
@@ -530,6 +542,9 @@ class GreedySynthesisClifford(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Clifford."""
+        if not isinstance(high_level_object, Clifford):
+            return None
+
         decomposition = synth_clifford_greedy(high_level_object)
         return decomposition
 
@@ -544,6 +559,9 @@ class LayerSynthesisClifford(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Clifford."""
+        if not isinstance(high_level_object, Clifford):
+            return None
+
         decomposition = synth_clifford_layers(high_level_object)
         return decomposition
 
@@ -559,6 +577,9 @@ class LayerLnnSynthesisClifford(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Clifford."""
+        if not isinstance(high_level_object, Clifford):
+            return None
+
         decomposition = synth_clifford_depth_lnn(high_level_object)
         return decomposition
 
@@ -572,6 +593,9 @@ class DefaultSynthesisLinearFunction(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given LinearFunction."""
+        if not isinstance(high_level_object, LinearFunction):
+            return None
+
         decomposition = synth_cnot_count_full_pmh(high_level_object.linear)
         return decomposition
 
@@ -595,11 +619,8 @@ class KMSSynthesisLinearFunction(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given LinearFunction."""
-
         if not isinstance(high_level_object, LinearFunction):
-            raise TranspilerError(
-                "PMHSynthesisLinearFunction only accepts objects of type LinearFunction"
-            )
+            return None
 
         use_inverted = options.get("use_inverted", False)
         use_transposed = options.get("use_transposed", False)
@@ -646,11 +667,8 @@ class PMHSynthesisLinearFunction(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given LinearFunction."""
-
         if not isinstance(high_level_object, LinearFunction):
-            raise TranspilerError(
-                "PMHSynthesisLinearFunction only accepts objects of type LinearFunction"
-            )
+            return None
 
         section_size = options.get("section_size", 2)
         use_inverted = options.get("use_inverted", False)
@@ -682,6 +700,9 @@ class KMSSynthesisPermutation(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Permutation."""
+        if not isinstance(high_level_object, PermutationGate):
+            return None
+
         decomposition = synth_permutation_depth_lnn_kms(high_level_object.pattern)
         return decomposition
 
@@ -695,6 +716,9 @@ class BasicSynthesisPermutation(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Permutation."""
+        if not isinstance(high_level_object, PermutationGate):
+            return None
+
         decomposition = synth_permutation_basic(high_level_object.pattern)
         return decomposition
 
@@ -708,6 +732,9 @@ class ACGSynthesisPermutation(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Permutation."""
+        if not isinstance(high_level_object, PermutationGate):
+            return None
+
         decomposition = synth_permutation_acg(high_level_object.pattern)
         return decomposition
 
@@ -858,6 +885,9 @@ class TokenSwapperSynthesisPermutation(HighLevelSynthesisPlugin):
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         """Run synthesis for the given Permutation."""
 
+        if not isinstance(high_level_object, PermutationGate):
+            return None
+
         trials = options.get("trials", 5)
         seed = options.get("seed", 0)
         parallel_threshold = options.get("parallel_threshold", 50)
@@ -1156,6 +1186,9 @@ class MCMTSynthesisDefault(HighLevelSynthesisPlugin):
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
         # first try to use the V-chain synthesis if enough auxiliary qubits are available
+        if not isinstance(high_level_object, MCMTGate):
+            return None
+
         if (
             decomposition := MCMTSynthesisVChain().run(
                 high_level_object, coupling_map, target, qubits, **options
@@ -1170,6 +1203,9 @@ class MCMTSynthesisNoAux(HighLevelSynthesisPlugin):
     """A V-chain based synthesis for ``MCMTGate``."""
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
+        if not isinstance(high_level_object, MCMTGate):
+            return None
+
         base_gate = high_level_object.base_gate
         ctrl_state = options.get("ctrl_state", None)
 
@@ -1195,6 +1231,9 @@ class MCMTSynthesisVChain(HighLevelSynthesisPlugin):
     """A V-chain based synthesis for ``MCMTGate``."""
 
     def run(self, high_level_object, coupling_map=None, target=None, qubits=None, **options):
+        if not isinstance(high_level_object, MCMTGate):
+            return None
+
         if options.get("num_clean_ancillas", 0) < high_level_object.num_ctrl_qubits - 1:
             return None  # insufficient number of auxiliary qubits
 

releasenotes/notes/fix-mcmt-to-gate-ec84e1c625312444.yaml

@@ -0,0 +1,15 @@
+---
+fixes:
+  - |
+    Fixed a bug where any instruction called ``"mcmt"`` would be passed into the high-level
+    synthesis routine for a :class:`.MCMTGate`, which causes a failure or invalid result.
+    In particular, this could happen accidentally when handling the :class:`.MCMT` _circuit_,
+    named ``"mcmt"``, and implicitly converting it into an instruction e.g. when appending 
+    it to a circuit.
+    Fixed `#13563 <https://github.com/Qiskit/qiskit/issues/13563>`__.
+upgrade_synthesis:
+  - |
+    The plugins for :class:`.LinearFunction` no longer raise an error if another object
+    than :class:`.LinearFunction` is passed into the ``run`` method. Instead, ``None`` is 
+    returned, which is consistent with the other plugins. If you relied on this error being raised,
+    you can manually perform an instance-check.

test/python/circuit/library/test_mcmt.py

@@ -285,6 +285,19 @@ def test_gate_with_parameters_vchain(self):
         self.assertEqual(circuit.num_parameters, 1)
         self.assertIs(circuit.parameters[0], theta)
 
+    def test_mcmt_circuit_as_gate(self):
+        """Test the MCMT plugin is only triggered for the gate, not the same-named circuit.
+
+        Regression test of #13563.
+        """
+        circuit = QuantumCircuit(2)
+        gate = RYGate(0.1)
+        mcmt = MCMT(gate=gate, num_ctrl_qubits=1, num_target_qubits=1)
+        circuit.append(mcmt, circuit.qubits)  # append the MCMT circuit as gate called "MCMT"
+
+        transpiled = transpile(circuit, basis_gates=["u", "cx"])
+        self.assertEqual(Operator(transpiled), Operator(gate.control(1)))
+
 
 if __name__ == "__main__":
     unittest.main()

test/python/transpiler/test_clifford_passes.py

@@ -831,6 +831,17 @@ def test_collect_all_clifford_gates(self):
         qct = PassManager(CollectCliffords(matrix_based=True)).run(qc)
         self.assertEqual(qct.count_ops()["clifford"], 1)
 
+    def test_plugin_unfortunate_name(self):
+        """Test the synthesis is not triggered for a custom gate with the same name."""
+        intruder = QuantumCircuit(2, name="clifford")
+        circuit = QuantumCircuit(2)
+        circuit.append(intruder.to_gate(), [0, 1])
+
+        hls = HighLevelSynthesis()
+        synthesized = hls(circuit)
+
+        self.assertIn("clifford", synthesized.count_ops())
+
 
 if __name__ == "__main__":
     unittest.main()

test/python/transpiler/test_high_level_synthesis.py

@@ -827,6 +827,17 @@ def test_plugin_selection_all_with_metrix(self):
             self.assertEqual(qct.size(), 24)
             self.assertEqual(qct.depth(), 13)
 
+    def test_unfortunate_name(self):
+        """Test the synthesis is not triggered for a custom gate with the same name."""
+        intruder = QuantumCircuit(2, name="linear_function")
+        circuit = QuantumCircuit(2)
+        circuit.append(intruder.to_gate(), [0, 1])
+
+        hls = HighLevelSynthesis()
+        synthesized = hls(circuit)
+
+        self.assertIn("linear_function", synthesized.count_ops())
+
 
 class TestKMSSynthesisLinearFunctionPlugin(QiskitTestCase):
     """Tests for the KMSSynthesisLinearFunction plugin for synthesizing linear functions."""
@@ -877,6 +888,17 @@ def test_invert_and_transpose(self):
             self.assertEqual(qct.size(), 87)
             self.assertEqual(qct.depth(), 32)
 
+    def test_unfortunate_name(self):
+        """Test the synthesis is not triggered for a custom gate with the same name."""
+        intruder = QuantumCircuit(2, name="linear_function")
+        circuit = QuantumCircuit(2)
+        circuit.append(intruder.to_gate(), [0, 1])
+
+        hls = HighLevelSynthesis()
+        synthesized = hls(circuit)
+
+        self.assertIn("linear_function", synthesized.count_ops())
+
 
 class TestTokenSwapperPermutationPlugin(QiskitTestCase):
     """Tests for the token swapper plugin for synthesizing permutation gates."""
@@ -1059,6 +1081,17 @@ def test_concrete_synthesis_all_permutations(self):
                 qubits = tuple(qc_transpiled.find_bit(q).index for q in inst.qubits)
                 self.assertIn(qubits, edges)
 
+    def test_unfortunate_name(self):
+        """Test the synthesis is not triggered for a custom gate with the same name."""
+        intruder = QuantumCircuit(2, name="permutation")
+        circuit = QuantumCircuit(2)
+        circuit.append(intruder.to_gate(), [0, 1])
+
+        hls = HighLevelSynthesis()
+        synthesized = hls(circuit)
+
+        self.assertIn("permutation", synthesized.count_ops())
+
 
 class TestHighLevelSynthesisModifiers(QiskitTestCase):
     """Tests for high-level-synthesis pass."""