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Improve performance of measure_all by inlining calls to barrier #10949

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Improve performance of measure_all by inlining calls to barrier #10949

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Improve performance of measure_all by inlining calls to barrier
eendebakpt Oct 3, 2023
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update comments
eendebakpt Oct 3, 2023
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fix pylint
eendebakpt Oct 12, 2023
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eendebakpt Nov 30, 2023
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eendebakpt Nov 30, 2023
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12 changes: 8 additions & 4 deletions qiskit/circuit/quantumcircuit.py
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@
from qiskit._accelerate.quantum_circuit import CircuitData
from qiskit.exceptions import QiskitError
from qiskit.utils.multiprocessing import is_main_process
from qiskit.circuit.barrier import Barrier
from qiskit.circuit.instruction import Instruction
from qiskit.circuit.gate import Gate
from qiskit.circuit.parameter import Parameter
Expand Down Expand Up @@ -2265,6 +2266,8 @@ def measure_all(
in the already existing classical bits, with qubit ``n`` being measured into classical bit
``n``.

A barrier gate is inserted before the measurement statements.

Returns a new circuit with measurements if ``inplace=False``.

Args:
Expand All @@ -2284,15 +2287,17 @@ def measure_all(
if add_bits:
new_creg = circ._create_creg(len(circ.qubits), "meas")
circ.add_register(new_creg)
circ.barrier()
# inline call to barrier
circ._append(Barrier(len(circ.qubits), label=None), circ.qubits, [])
circ.measure(circ.qubits, new_creg)
else:
if len(circ.clbits) < len(circ.qubits):
raise CircuitError(
"The number of classical bits must be equal or greater than "
"the number of qubits."
)
circ.barrier()
# inline call to barrier
circ._append(Barrier(len(circ.qubits), label=None), circ.qubits, [])
circ.measure(circ.qubits, circ.clbits[0 : len(circ.qubits)])

if not inplace:
Expand Down Expand Up @@ -2815,14 +2820,13 @@ def barrier(self, *qargs: QubitSpecifier, label=None) -> InstructionSet:
Returns:
qiskit.circuit.InstructionSet: handle to the added instructions.
"""
from .barrier import Barrier

qubits = (
# This uses a `dict` not a `set` to guarantee a deterministic order to the arguments.
list({q: None for qarg in qargs for q in self.qbit_argument_conversion(qarg)})
if qargs
else self.qubits.copy()
)

return self.append(Barrier(len(qubits), label=label), qubits, [])

def delay(
Expand Down