SIGABRT Error with DelayMeasures Pass on Certain Circuits

[p51lee]

Overview

Applying a DelayMeasures compilation pass to a specific circuit will result in a SIGABRT exit when accessing the circuit later.

Example and reproduction steps

Consider the following Python code:

import pytket
from pytket.passes import DelayMeasures

circuit_tket = pytket.Circuit(4, 4)
circuit_tket.CX(0, 1)
circuit_tket.Measure(3, 1)
circuit_tket.Measure(1, 1)
circuit_tket.X(1)
circuit_tket.CCX(1, 3, 2)
circuit_tket.Measure(2, 2)

# Apply the DelayMeasures pass to the circuit
print(DelayMeasures().apply(circuit_tket))

# Attempt to print the commands of the modified circuit
print(circuit_tket.get_commands())

Observed

Executing the above code results in a critical assertion failure and the process terminates unexpectedly with a SIGABRT signal:

True
[tket] [critical] Assertion '!"slice is empty"' (../../src/Circuit/macro_circ_info.cpp : operator++ : 935) failed.  Aborting.

Process finished with exit code 134 (interrupted by signal 6:SIGABRT)