Simulator can run indefinately when running circuits with conditionals #2230
Description
Benny and I found this bug.
Informations
- Qiskit Aer version: 0.15.0
- Python version: 3.11.6
- Operating system: Ubuntu 23.01 LTS
What is the current behavior?
Runs indefinately
Steps to reproduce the problem
Run this code:
from qiskit import QuantumCircuit, ClassicalRegister
from helpers.qiskit_helpers import compare_statevectors, run_on_simulator, run_routing_simulation
subcirc1 = QuantumCircuit(0)
# subcirc1.x(0)
main_circ = QuantumCircuit(1)
# Adding creg resources
creg_0 = ClassicalRegister(1)
main_circ.add_register(creg_0)
main_circ.measure(0, creg_0[0])
main_circ.x(0)
with main_circ.if_test((creg_0[0],0)) as else_1:
main_circ.append(subcirc1)
with else_1:
main_circ.append(subcirc1)
main_circ.measure_active()
print(main_circ)
run_on_simulator(main_circ, 1)Making the subroutine non-empty makes it work
from qiskit import QuantumCircuit, ClassicalRegister
from helpers.qiskit_helpers import compare_statevectors, run_on_simulator, run_routing_simulation
subcirc1 = QuantumCircuit(1)
subcirc1.x(0)
main_circ = QuantumCircuit(1)
# Adding creg resources
creg_0 = ClassicalRegister(1)
main_circ.add_register(creg_0)
main_circ.measure(0, creg_0[0])
main_circ.x(0)
with main_circ.if_test((creg_0[0],0)) as else_1:
main_circ.append(subcirc1, [0])
with else_1:
main_circ.append(subcirc1, [0])
main_circ.measure_active()
print(main_circ)
run_on_simulator(main_circ, 1)Moving the x gate before the measure makes it work
from qiskit import QuantumCircuit, ClassicalRegister
from helpers.qiskit_helpers import compare_statevectors, run_on_simulator, run_routing_simulation
subcirc1 = QuantumCircuit(0)
main_circ = QuantumCircuit(1)
# Adding creg resources
creg_0 = ClassicalRegister(1)
main_circ.add_register(creg_0)
main_circ.x(0)
main_circ.measure(0, creg_0[0])
with main_circ.if_test((creg_0[0],0)) as else_1:
main_circ.append(subcirc1)
with else_1:
main_circ.append(subcirc1)
main_circ.measure_active()
print(main_circ)
run_on_simulator(main_circ, 1)What is the expected behavior?
Should return results, in the case of empty subroutine, should always treat it as identity