Add support for delay instruction

* The backend-dependent time unit dt is left untouched
* All other time units (s, ms, us, ns, ps) are converted to us when
  generating QIR

src/qiskit_qir/visitor.py

@@ -52,6 +52,7 @@
     "cz",
     "h",
     "reset",
+    "delay",
     "rx",
     "ry",
     "rz",
@@ -75,6 +76,7 @@
     "m",
     "measure",
     "reset",
+    "delay",
     "rx",
     "ry",
     "rz",
@@ -88,9 +90,7 @@
     "z",
 ]
 
-_NOOP_INSTRUCTIONS = ["delay"]
-
-_SUPPORTED_INSTRUCTIONS = _QUANTUM_INSTRUCTIONS + _NOOP_INSTRUCTIONS
+_SUPPORTED_INSTRUCTIONS = _QUANTUM_INSTRUCTIONS
 
 
 class QuantumCircuitElementVisitor(metaclass=ABCMeta):
@@ -311,7 +311,13 @@ def __branch():
                 if self._emit_barrier_calls:
                     qis.barrier(self._builder)
             elif "delay" == instruction.name:
-                pass
+                # us is chosen as the default time unit in QIR since it is well
+                # suited to current performance of qubit implementations.
+                # When using dt, the backend-dependent time unit, the duration
+                # value is left untouched.
+                multipliers = {"s": 1e6, "ms": 1e3, "us": 1, "ns": 1e-3, "ps": 1e-6, "dt": 1}
+                duration = instruction.duration * multipliers[instruction.unit]
+                qis.delay(self._builder, duration, *qubits)
             elif "swap" == instruction.name:
                 qis.swap(self._builder, *qubits)
             elif "ccx" == instruction.name:

tests/test_circuits/basic_gates.py

@@ -25,6 +25,8 @@
 
 _measurements = {"measure": "mz"}
 
+_delays = {"delay": "delay"}
+
 _rotations = {"rx": "rx", "ry": "ry", "rz": "rz"}
 
 _two_qubit_gates = {"cx": "cnot", "cz": "cz", "swap": "swap"}
@@ -43,6 +45,8 @@ def _map_gate_name(gate: str) -> str:
         return _adj_gates[gate]
     elif gate in _measurements:
         return _measurements[gate]
+    elif gate in _delays:
+        return _delays[gate]
     elif gate in _rotations:
         return _rotations[gate]
     elif gate in _two_qubit_gates:
@@ -76,6 +80,27 @@ def test_fixture():
     locals()[name] = _generate_one_qubit_fixture(gate)
 
 
+def _generate_delay_gate_fixture(unit: str):
+    @pytest.fixture()
+    def test_fixture():
+        circuit = QuantumCircuit(1)
+        if unit == 'dt':
+            circuit.delay(1, 0, unit=unit)
+        else:
+            circuit.delay(0.5, 0, unit=unit)
+        return _map_gate_name('delay'), unit, circuit
+
+    return test_fixture
+
+
+delay_tests = []
+# Generate time param operation fixtures
+for unit in {'s', 'ms', 'us', 'ns', 'ps', 'dt'}:
+    name = _fixture_name('delay_' + unit)
+    delay_tests.append(name)
+    locals()[name] = _generate_delay_gate_fixture(unit)
+
+
 def _generate_rotation_fixture(gate: str):
     @pytest.fixture()
     def test_fixture():

tests/test_qiskit_qir.py

@@ -16,6 +16,7 @@
 from test_circuits.basic_gates import (
     single_op_tests,
     adj_op_tests,
+    delay_tests,
     rotation_tests,
     double_op_tests,
     triple_op_tests,
@@ -112,6 +113,7 @@ def test_adj_gates(circuit_name, request):
 def test_rotation_gates(circuit_name, request):
     qir_op, circuit = request.getfixturevalue(circuit_name)
     generated_qir = str(to_qir_module(circuit)[0]).splitlines()
+    print(generated_qir)
     test_utils.check_attributes(generated_qir, 1, 0)
     func = test_utils.get_entry_point_body(generated_qir)
     assert func[0] == test_utils.initialize_call_string()
@@ -120,6 +122,25 @@ def test_rotation_gates(circuit_name, request):
     assert len(func) == 3
 
 
+@pytest.mark.parametrize("circuit_name", delay_tests)
+def test_delay_gate(circuit_name, request):
+    qir_op, unit, circuit = request.getfixturevalue(circuit_name)
+    generated_qir = str(to_qir_module(circuit)[0]).splitlines()
+    print(circuit)
+    print(generated_qir)
+    test_utils.check_attributes(generated_qir, 1, 0)
+    func = test_utils.get_entry_point_body(generated_qir)
+    assert func[0] == test_utils.initialize_call_string()
+    if  unit == 'dt':
+        assert func[1] == test_utils.rotation_call_string(qir_op, 1, 0)
+    else:
+        multipliers = {"s": 1e6, "ms": 1e3, "us": 1, "ns": 1e-3, "ps": 1e-6}
+        duration = 0.5 * multipliers[unit]
+        assert func[1] == test_utils.rotation_call_string(qir_op, duration, 0)
+    assert func[2] == test_utils.return_string()
+    assert len(func) == 3
+
+
 @pytest.mark.parametrize("circuit_name", double_op_tests)
 def test_double_qubit_gates(circuit_name, request):
     qir_op, circuit = request.getfixturevalue(circuit_name)