Faulty conditioning on classical registers

[daniel-mills-cqc]

The following is has 3 X gates, each controlled on the same classical wire. The first and third X gates are turned on, but the middle X gate is off. The expected result would be the 0 state, but the outcome is 1.

from pytket import Circuit
from pytket.extensions.quantinuum import QuantinuumBackend, QuantinuumAPIOffline

circuit = Circuit(1)

control_reg = circuit.add_c_register(name="control", size=1)
meas_reg = circuit.add_c_register(name="measure", size=1)

circuit.add_c_setreg(1, control_reg)
circuit.X(0, condition=control_reg[0])

circuit.add_c_setreg(0, control_reg)
circuit.X(0, condition=control_reg[0])

circuit.add_c_setreg(1, control_reg)
circuit.X(0, condition=control_reg[0])

circuit.Measure(
    qubit=circuit.qubits[0],
    bit=meas_reg[0],
)

api_offline = QuantinuumAPIOffline()
backend = QuantinuumBackend(
    device_name="H1-1LE",
   api_handler = api_offline,
)
compiled_circuit = backend.get_compiled_circuit(circuit, optimisation_level=0)
result = backend.run_circuit(
    compiled_circuit, 
    n_shots=100,
    no_opt=True
)
result.get_counts(meas_reg)

Gives

Counter({(1,): 1})

[cqc-alec]

Suspected cause: https://github.com/CQCL/pytket-phir/issues/150