Singletonized Measure and Reset instructions (#11170)

* Singletonized 'Measure' and 'Reset' instructions and drafted a release note

* Added singleton key functionality and test cases for Measure() and Reset() singleton instructions

* Implemented corrections from review on test_singleton module

qiskit/circuit/measure.py

@@ -14,17 +14,19 @@
 Quantum measurement in the computational basis.
 """
 
-from qiskit.circuit.instruction import Instruction
+from qiskit.circuit.singleton import SingletonInstruction, stdlib_singleton_key
 from qiskit.circuit.exceptions import CircuitError
 
 
-class Measure(Instruction):
+class Measure(SingletonInstruction):
     """Quantum measurement in the computational basis."""
 
     def __init__(self, label=None, *, duration=None, unit="dt"):
         """Create new measurement instruction."""
         super().__init__("measure", 1, 1, [], label=label, duration=duration, unit=unit)
 
+    _singleton_lookup_key = stdlib_singleton_key()
+
     def broadcast_arguments(self, qargs, cargs):
         qarg = qargs[0]
         carg = cargs[0]

qiskit/circuit/quantumcircuit.py

@@ -59,8 +59,6 @@
 from .bit import Bit
 from .quantumcircuitdata import QuantumCircuitData, CircuitInstruction
 from .delay import Delay
-from .measure import Measure
-from .reset import Reset
 
 if typing.TYPE_CHECKING:
     import qiskit  # pylint: disable=cyclic-import
@@ -2180,6 +2178,8 @@ def reset(self, qubit: QubitSpecifier) -> InstructionSet:
         Returns:
             qiskit.circuit.InstructionSet: handle to the added instruction.
         """
+        from .reset import Reset
+
         return self.append(Reset(), [qubit], [])
 
     def measure(self, qubit: QubitSpecifier, cbit: ClbitSpecifier) -> InstructionSet:
@@ -2255,6 +2255,8 @@ def measure(self, qubit: QubitSpecifier, cbit: ClbitSpecifier) -> InstructionSet
                 circuit.measure(qreg[1], creg[1])
 
         """
+        from .measure import Measure
+
         return self.append(Measure(), [qubit], [cbit])
 
     def measure_active(self, inplace: bool = True) -> Optional["QuantumCircuit"]:

qiskit/circuit/reset.py

@@ -14,16 +14,18 @@
 Qubit reset to computational zero.
 """
 
-from qiskit.circuit.instruction import Instruction
+from qiskit.circuit.singleton import SingletonInstruction, stdlib_singleton_key
 
 
-class Reset(Instruction):
+class Reset(SingletonInstruction):
     """Qubit reset."""
 
     def __init__(self, label=None, *, duration=None, unit="dt"):
         """Create new reset instruction."""
         super().__init__("reset", 1, 0, [], label=label, duration=duration, unit=unit)
 
+    _singleton_lookup_key = stdlib_singleton_key()
+
     def broadcast_arguments(self, qargs, cargs):
         for qarg in qargs[0]:
             yield [qarg], []

qiskit/qasm2/parse.py

@@ -234,15 +234,13 @@ def from_bytecode(bytecode, custom_instructions: Iterable[CustomInstruction]):
             qc._append(CircuitInstruction(Measure(), (qubits[qubit],), (clbits[clbit],)))
         elif opcode == OpCode.ConditionedMeasure:
             qubit, clbit, creg, value = op.operands
-            measure = Measure()
-            measure.condition = (qc.cregs[creg], value)
+            measure = Measure().c_if(qc.cregs[creg], value)
             qc._append(CircuitInstruction(measure, (qubits[qubit],), (clbits[clbit],)))
         elif opcode == OpCode.Reset:
             qc._append(CircuitInstruction(Reset(), (qubits[op.operands[0]],)))
         elif opcode == OpCode.ConditionedReset:
             qubit, creg, value = op.operands
-            reset = Reset()
-            reset.condition = (qc.cregs[creg], value)
+            reset = Reset().c_if(qc.cregs[creg], value)
             qc._append(CircuitInstruction(reset, (qubits[qubit],)))
         elif opcode == OpCode.Barrier:
             op_qubits = op.operands[0]

releasenotes/notes/singletonize-instructions-78723f68cd0ac03f.yaml

@@ -0,0 +1,32 @@
+---
+features:
+  - |
+    The following standard library instructions are now instances of
+    :class:`~.SingletonInstruction`:
+    
+     * :class:`~.Measure`
+     * :class:`~.Reset`
+    
+    This means that if these classes are instantiated as (e.g.) ``Measure()`` using
+    all the constructor defaults, they will all share a single global
+    instance. This results in large reduction in the memory overhead for > 1
+    object of these types and significantly faster object construction time.
+upgrade:
+  - |
+    The following standard library instructions:
+    
+     * :class:`~.Measure`
+     * :class:`~.Reset`
+     
+    are immutable, unless the attributes ``label``, ``duration`` and ``unit`` are given as keyword 
+    arguments during class construction. 
+    The attributes :attr:`~.Instruction.label`, :attr:`~.Instruction.duration`, :attr:`~.Instruction.unit`, 
+    and :attr:`~.Instruction.condition` attributes are all not publicly accessible and setting these attributes
+    directly is not allowed and it will raise an exception. If they are needed for a particular
+    instance you must ensure you have a mutable instance using :meth:`.Instruction.to_mutable`
+    and use :meth:`.Instruction.c_if` for :attr:`~.Instruction.condition`
+    For the singleton variant of these instructions, there is a special attribute 
+    :attr:`~.SingletonInstruction._singleton_lookup_key`, that when called generates a key based on the input
+    arguments, which can be used for identifying and indexing these instructions within the framework. 
+    
+    

test/python/circuit/test_singleton.py

@@ -14,7 +14,7 @@
 
 
 """
-Tests for singleton gate behavior
+Tests for singleton gate and instruction behavior
 """
 
 import copy
@@ -36,15 +36,16 @@
     XGate,
     C4XGate,
 )
+from qiskit.circuit import Measure, Reset
 from qiskit.circuit import Clbit, QuantumCircuit, QuantumRegister, ClassicalRegister
-from qiskit.circuit.singleton import SingletonGate, SingletonInstruction
+from qiskit.circuit.singleton import SingletonGate
 from qiskit.converters import dag_to_circuit, circuit_to_dag
 
 from qiskit.test.base import QiskitTestCase
 
 
-class TestSingletonGate(QiskitTestCase):
-    """Qiskit SingletonGate tests."""
+class TestSingleton(QiskitTestCase):
+    """Qiskit SingletonGate and SingletonInstruction tests."""
 
     def test_default_singleton(self):
         gate = HGate()
@@ -325,20 +326,38 @@ def __init__(self, x):
         self.assertEqual(gate.x, 1)
         self.assertIsNot(MyAbstractGate(1), MyAbstractGate(1))
 
-    def test_inherit_singleton(self):
-        class Measure(SingletonInstruction):
-            def __init__(self):
-                super().__init__("measure", 1, 1, [])
+    def test_return_type_singleton_instructions(self):
+        measure = Measure()
+        new_measure = Measure()
+        self.assertIs(measure, new_measure)
+        self.assertIs(measure.base_class, Measure)
+        self.assertIsInstance(measure, Measure)
+
+        reset = Reset()
+        new_reset = Reset()
+        self.assertIs(reset, new_reset)
+        self.assertIs(reset.base_class, Reset)
+        self.assertIsInstance(reset, Reset)
+
+    def test_singleton_instruction_integration(self):
+        measure = Measure()
+        reset = Reset()
+        qc = QuantumCircuit(1, 1)
+        qc.measure(0, 0)
+        qc.reset(0)
+        self.assertIs(qc.data[0].operation, measure)
+        self.assertIs(qc.data[1].operation, reset)
 
+    def test_inherit_singleton_instructions(self):
         class ESPMeasure(Measure):
             pass
 
-        base = Measure()
-        esp = ESPMeasure()
-        self.assertIs(esp, ESPMeasure())
-        self.assertIsNot(esp, base)
-        self.assertIs(base.base_class, Measure)
-        self.assertIs(esp.base_class, ESPMeasure)
+        measure_base = Measure()
+        esp_measure = ESPMeasure()
+        self.assertIs(esp_measure, ESPMeasure())
+        self.assertIsNot(esp_measure, measure_base)
+        self.assertIs(measure_base.base_class, Measure)
+        self.assertIs(esp_measure.base_class, ESPMeasure)
 
     def test_singleton_with_default(self):
         # Explicitly setting the label to its default.