make commutative_cancellation basis aware (Qiskit#5672)

* fixes Qiskit#5644 * move change to commutation analysis to new pr. * Update qiskit/transpiler/passes/optimization/commutative_cancellation.py Co-authored-by: Kevin Krsulich <kevin@krsulich.net> * Update qiskit/transpiler/passes/optimization/commutative_cancellation.py Co-authored-by: Kevin Krsulich <kevin@krsulich.net> * Update qiskit/transpiler/passes/optimization/commutative_cancellation.py Co-authored-by: Kevin Krsulich <kevin@krsulich.net> * Update qiskit/transpiler/passes/optimization/commutative_cancellation.py Co-authored-by: Kevin Krsulich <kevin@krsulich.net> * check global phase * minor fix * preserve global phase in commutative_cancellation * Update test/python/transpiler/test_commutative_cancellation.py Co-authored-by: Kevin Krsulich <kevin@krsulich.net> * add blank line * add release note Co-authored-by: Kevin Krsulich <kevin@krsulich.net> Co-authored-by: Luciano Bello <bel@zurich.ibm.com> Co-authored-by: Kevin Krsulich <kevin.krsulich@ibm.com>
lcapelluto · Mar 3, 2021 · 0d85759 · 0d85759
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diff --git a/qiskit/transpiler/passes/optimization/commutative_cancellation.py b/qiskit/transpiler/passes/optimization/commutative_cancellation.py
@@ -22,6 +22,9 @@
 from qiskit.dagcircuit import DAGCircuit
 from qiskit.circuit.library.standard_gates.u1 import U1Gate
 from qiskit.circuit.library.standard_gates.rx import RXGate
+from qiskit.circuit.library.standard_gates.p import PhaseGate
+from qiskit.circuit.library.standard_gates.rz import RZGate
+
 
 _CUTOFF_PRECISION = 1E-5
 
@@ -35,8 +38,22 @@ class CommutativeCancellation(TransformationPass):
         H, X, Y, Z, CX, CY, CZ
     """
 
-    def __init__(self):
+    def __init__(self, basis_gates=None):
+        """
+        CommutativeCancellation initializer.
+
+        Args:
+            basis_gates (list[str]): Basis gates to consider, e.g. `['u3', 'cx']`. For the effects
+                of this pass, the basis is the set intersection between the `basis` parameter
+                and the gates in the dag.
+        """
         super().__init__()
+        if basis_gates:
+            self.basis = set(basis_gates)
+        else:
+            self.basis = set()
+
+        self._var_z_map = {'rz': RZGate, 'p': PhaseGate, 'u1': U1Gate}
         self.requires.append(CommutationAnalysis())
 
     def run(self, dag):
@@ -51,6 +68,18 @@ def run(self, dag):
         Raises:
             TranspilerError: when the 1-qubit rotation gates are not found
         """
+        var_z_gate = None
+        z_var_gates = [gate for gate in dag.count_ops().keys()
+                       if gate in self._var_z_map]
+        if z_var_gates:
+            # priortize z gates in circuit
+            var_z_gate = self._var_z_map[next(iter(z_var_gates))]
+        else:
+            z_var_gates = [gate for gate in self.basis
+                           if gate in self._var_z_map]
+            if z_var_gates:
+                var_z_gate = self._var_z_map[next(iter(z_var_gates))]
+
         # Now the gates supported are hard-coded
         q_gate_list = ['cx', 'cy', 'cz', 'h', 'y']
 
@@ -75,7 +104,7 @@ def run(self, dag):
                     num_qargs = len(node.qargs)
                     if num_qargs == 1 and node.name in q_gate_list:
                         cancellation_sets[(node.name, wire, com_set_idx)].append(node)
-                    if num_qargs == 1 and node.name in ['z', 'u1', 'rz', 't', 's']:
+                    if num_qargs == 1 and node.name in ['p', 'z', 'u1', 'rz', 't', 's']:
                         cancellation_sets[('z_rotation', wire, com_set_idx)].append(node)
                     if num_qargs == 1 and node.name in ['rx', 'x']:
                         cancellation_sets[('x_rotation', wire, com_set_idx)].append(node)
@@ -88,6 +117,8 @@ def run(self, dag):
                         cancellation_sets[q2_key].append(node)
 
         for cancel_set_key in cancellation_sets:
+            if cancel_set_key[0] == 'z_rotation' and var_z_gate is None:
+                continue
             set_len = len(cancellation_sets[cancel_set_key])
             if set_len > 1 and cancel_set_key[0] in q_gate_list:
                 gates_to_cancel = cancellation_sets[cancel_set_key]
@@ -98,13 +129,14 @@ def run(self, dag):
                 run = cancellation_sets[cancel_set_key]
                 run_qarg = run[0].qargs[0]
                 total_angle = 0.0  # lambda
+                total_phase = 0.0
                 for current_node in run:
                     if (current_node.condition is not None
                             or len(current_node.qargs) != 1
                             or current_node.qargs[0] != run_qarg):
                         raise TranspilerError("internal error")
 
-                    if current_node.name in ['u1', 'rz', 'rx']:
+                    if current_node.name in ['p', 'u1', 'rz', 'rx']:
                         current_angle = float(current_node.op.params[0])
                     elif current_node.name in ['z', 'x']:
                         current_angle = np.pi
@@ -115,19 +147,26 @@ def run(self, dag):
 
                     # Compose gates
                     total_angle = current_angle + total_angle
+                    if current_node.op.definition:
+                        total_phase += current_node.op.definition.global_phase
 
                 # Replace the data of the first node in the run
                 if cancel_set_key[0] == 'z_rotation':
-                    new_op = U1Gate(total_angle)
+                    new_op = var_z_gate(total_angle)
                 elif cancel_set_key[0] == 'x_rotation':
                     new_op = RXGate(total_angle)
 
+                new_op_phase = 0
                 if np.mod(total_angle, (2 * np.pi)) > _CUTOFF_PRECISION:
                     new_qarg = QuantumRegister(1, 'q')
                     new_dag = DAGCircuit()
                     new_dag.add_qreg(new_qarg)
                     new_dag.apply_operation_back(new_op, [new_qarg[0]])
                     dag.substitute_node_with_dag(run[0], new_dag)
+                    if new_op.definition:
+                        new_op_phase = new_op.definition.global_phase
+
+                dag.global_phase = total_phase - new_op_phase
 
                 # Delete the other nodes in the run
                 for current_node in run[1:]:

diff --git a/qiskit/transpiler/preset_passmanagers/level2.py b/qiskit/transpiler/preset_passmanagers/level2.py
@@ -174,7 +174,8 @@ def _direction_condition(property_set):
     def _opt_control(property_set):
         return not property_set['depth_fixed_point']
 
-    _opt = [Optimize1qGatesDecomposition(basis_gates), CommutativeCancellation()]
+    _opt = [Optimize1qGatesDecomposition(basis_gates),
+            CommutativeCancellation(basis_gates=basis_gates)]
 
     # 9. Schedule the circuit only when scheduling_method is supplied
     if scheduling_method:

diff --git a/releasenotes/notes/basis_aware_commutative_cancellation-9f3b4924b0fa478d.yaml b/releasenotes/notes/basis_aware_commutative_cancellation-9f3b4924b0fa478d.yaml
@@ -0,0 +1,13 @@
+---
+upgrade:
+  - |
+    This makes it optionally possible to tell the
+    :class:`qiskit.transpiler.passes.optimization.CommutativeCancellation`
+    pass about target basis. Previously the pass would automatically
+    replace consecutive gates which commute with ZGate with the
+    U1Gate. Functionally the target basis is the union of the gates in
+    the circuit and the target basis. If no variable z-rotation gate
+    exists no commutative cancellation will occur. This change may
+    lead to different behavior if using this pass without specifying a
+    basis and supplying a circuit with no variable z-rotation gate so
+    a basis gate should be explicitly supplied.
diff --git a/test/python/transpiler/test_commutative_cancellation.py b/test/python/transpiler/test_commutative_cancellation.py
@@ -17,9 +17,10 @@
 from qiskit.test import QiskitTestCase
 
 from qiskit import QuantumRegister, QuantumCircuit
-from qiskit.circuit.library import U1Gate
+from qiskit.circuit.library import U1Gate, RZGate
 from qiskit.transpiler import PassManager, PropertySet
 from qiskit.transpiler.passes import CommutationAnalysis, CommutativeCancellation, FixedPoint, Size
+from qiskit.quantum_info import Operator
 
 
 class TestCommutativeCancellation(QiskitTestCase):
@@ -71,7 +72,7 @@ def test_all_gates(self):
         new_circuit = passmanager.run(circuit)
 
         expected = QuantumCircuit(qr)
-        expected.append(U1Gate(2.0), [qr[0]])
+        expected.append(RZGate(2.0), [qr[0]])
         expected.rx(1.0, qr[0])
 
         self.assertEqual(expected, new_circuit)
@@ -368,9 +369,9 @@ def test_commutative_circuit2(self):
         passmanager.append(CommutativeCancellation())
         new_circuit = passmanager.run(circuit)
         expected = QuantumCircuit(qr)
-        expected.append(U1Gate(np.pi * 17 / 12), [qr[2]])
+        expected.append(RZGate(np.pi * 17 / 12), [qr[2]])
         expected.cx(qr[2], qr[1])
-
+        expected.global_phase = (np.pi * 17 / 12 - (2 * np.pi / 3)) / 2
         self.assertEqual(expected, new_circuit)
 
     def test_commutative_circuit3(self):
@@ -412,8 +413,8 @@ def test_commutative_circuit3(self):
                            do_while=lambda property_set: not property_set['size_fixed_point'])
         new_circuit = passmanager.run(circuit)
         expected = QuantumCircuit(qr)
-        expected.append(U1Gate(np.pi * 17 / 12), [qr[2]])
-        expected.append(U1Gate(np.pi * 2 / 3), [qr[3]])
+        expected.append(RZGate(np.pi * 17 / 12), [qr[2]])
+        expected.append(RZGate(np.pi * 2 / 3), [qr[3]])
         expected.cx(qr[2], qr[1])
 
         self.assertEqual(expected, new_circuit)
@@ -524,6 +525,86 @@ def test_conditional_gates_dont_commute(self):
 
         self.assertEqual(circuit, new_circuit)
 
+    def test_basis_01(self):
+        """Test basis priority change, phase gate"""
+        circuit = QuantumCircuit(1)
+        circuit.s(0)
+        circuit.z(0)
+        circuit.t(0)
+        circuit.rz(np.pi, 0)
+        passmanager = PassManager()
+        passmanager.append(CommutativeCancellation(basis_gates=['cx', 'p', 'sx']))
+        new_circuit = passmanager.run(circuit)
+        expected = QuantumCircuit(1)
+        expected.rz(11 * np.pi / 4, 0)
+        expected.global_phase = 11 * np.pi / 4 / 2 - np.pi / 2
+
+        self.assertEqual(new_circuit, expected)
+
+    def test_basis_02(self):
+        """Test basis priority change, Rz gate"""
+        circuit = QuantumCircuit(1)
+        circuit.s(0)
+        circuit.z(0)
+        circuit.t(0)
+        passmanager = PassManager()
+        passmanager.append(CommutativeCancellation(basis_gates=['cx', 'rz', 'sx']))
+        new_circuit = passmanager.run(circuit)
+
+        expected = QuantumCircuit(1)
+        expected.rz(7 * np.pi / 4, 0)
+        expected.global_phase = 7 * np.pi / 4 / 2
+        self.assertEqual(new_circuit, expected)
+
+    def test_basis_03(self):
+        """Test no specified basis"""
+        circuit = QuantumCircuit(1)
+        circuit.s(0)
+        circuit.z(0)
+        circuit.t(0)
+        passmanager = PassManager()
+        passmanager.append(CommutativeCancellation())
+        new_circuit = passmanager.run(circuit)
+
+        expected = QuantumCircuit(1)
+        expected.s(0)
+        expected.z(0)
+        expected.t(0)
+        self.assertEqual(new_circuit, expected)
+
+    def test_basis_global_phase_01(self):
+        """Test no specified basis, rz"""
+        circ = QuantumCircuit(1)
+        circ.rz(np.pi/2, 0)
+        circ.p(np.pi/2, 0)
+        circ.p(np.pi/2, 0)
+        passmanager = PassManager()
+        passmanager.append(CommutativeCancellation())
+        ccirc = passmanager.run(circ)
+        self.assertEqual(Operator(circ), Operator(ccirc))
+
+    def test_basis_global_phase_02(self):
+        """Test no specified basis, p"""
+        circ = QuantumCircuit(1)
+        circ.p(np.pi/2, 0)
+        circ.rz(np.pi/2, 0)
+        circ.p(np.pi/2, 0)
+        passmanager = PassManager()
+        passmanager.append(CommutativeCancellation())
+        ccirc = passmanager.run(circ)
+        self.assertEqual(Operator(circ), Operator(ccirc))
+
+    def test_basis_global_phase_03(self):
+        """Test global phase preservation if cummulative z-rotation is 0"""
+        circ = QuantumCircuit(1)
+        circ.rz(np.pi/2, 0)
+        circ.p(np.pi/2, 0)
+        circ.z(0)
+        passmanager = PassManager()
+        passmanager.append(CommutativeCancellation())
+        ccirc = passmanager.run(circ)
+        self.assertEqual(Operator(circ), Operator(ccirc))
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/test/python/transpiler/test_passmanager.py b/test/python/transpiler/test_passmanager.py
@@ -97,7 +97,7 @@ def callback(**kwargs):
             calls.append(out_dict)
 
         passmanager = PassManager()
-        passmanager.append(CommutativeCancellation())
+        passmanager.append(CommutativeCancellation(basis_gates=['u1', 'u2', 'u3', 'cx']))
         passmanager.run(circuit, callback=callback)
         self.assertEqual(len(calls), 2)
         self.assertEqual(len(calls[0]), 5)