Critical Assertion in LexiRoute.cpp when using RoutingPass

[nquetschlich]

Hi,

I am combining qiskit and TKET compilation passes together in a single compilation flow and for some quantum circuits, I sometimes get the following critical assertion leading to an abort of the python script.

[2023-01-17 09:14:13] [tket] [critical] Assertion 'jt != architecture_nodes.end()' (/Users/alec/.conan/data/tket/1.0.36/tket/stable/build/59ebf0620228eb658575009636eae68dcd1b80d6/Mapping/LexiRoute.cpp : reassign_node : 58) failed. Aborting.

The behavior can be reproduced by the (rather lengthy) code example:

from qiskit.circuit.equivalence_library import StandardEquivalenceLibrary
from qiskit.transpiler.passes import (
    ApplyLayout,
    BasisTranslator,
    EnlargeWithAncilla,
    FullAncillaAllocation,
    SabreLayout,
)
from qiskit.transpiler import CouplingMap, PassManager
from qiskit.providers.fake_provider import FakeMontreal
from qiskit import QuantumCircuit

from pytket.passes import (
    RoutingPass,
)
from pytket import architecture
from pytket.extensions.qiskit import qiskit_to_tk, tk_to_qiskit


cmap = FakeMontreal().configuration().coupling_map


def MyBasisTranslator(qc):
    transpile_pass = BasisTranslator(StandardEquivalenceLibrary, target_basis=["rz", "sx", "x", "cx", "measure"])
    pm = PassManager(transpile_pass)
    qc = pm.run(qc)
    return qc


def MySabreLayout(qc):
    transpile_pass = [
        SabreLayout(coupling_map=CouplingMap(cmap)),
        FullAncillaAllocation(coupling_map=CouplingMap(cmap)),
        EnlargeWithAncilla(),
        ApplyLayout(),
    ]
    pm = PassManager(transpile_pass)
    qc = pm.run(qc)
    return qc


def MyRoutingPass(qc):
    tket_pass = RoutingPass(architecture.Architecture(cmap))
    tket_qc = qiskit_to_tk(qc)
    tket_pass.apply(tket_qc)
    return tk_to_qiskit(tket_qc)


for i in range (1000):
    print(i)
    qasm_str = 'OPENQASM 2.0; include "qelib1.inc";qreg q[20];creg meas[20];h q[0];h q[1];cz q[0],q[1];h q[2];h q[3];cz q[2],q[3];h q[4];h q[5];cz q[4],q[5];h q[6];h q[7];cz q[6],q[7];h q[8];h q[9];cz q[8],q[9];h q[10];cz q[3],q[10];cz q[9],q[10];h q[11];cz q[7],q[11];h q[12];cz q[2],q[12];h q[13];cz q[5],q[13];h q[14];cz q[12],q[14];cz q[13],q[14];h q[15];cz q[6],q[15];cz q[11],q[15];h q[16];cz q[0],q[16];cz q[8],q[16];h q[17];h q[18];cz q[1],q[18];cz q[17],q[18];h q[19];cz q[4],q[19];cz q[17],q[19];'
    qc = QuantumCircuit.from_qasm_str(qasm_str)

    qc = MyBasisTranslator(qc)
    qc = MySabreLayout(qc)
    qc = MyRoutingPass(qc)

The error occurs not always, when executing the script it usually happens before iteration 30.
Also, it happens for different target devices and corresponding cmaps. Interestingly, the error says node 58 although IBM Montreal is a 27 qubit device and the printed path obviously does not correspond to a valid path on my computer, even the mentioned TKET version within the printed path is outdated.

I use pytket v1.10.0, qiskit v0.39.4, python 3.10.8 and Mac OS 13.1.

[sjdilkes]

Good morning @nquetschlich, thank you very much for bringing this issue to our attention.

This is actually a known bug with an open pull request for its fix at #715. If you're interested, hopefully the description of the issue in that pull request will explain what was going wrong.

I have run your example locally using a build of TKET from this linked branch and the script passes (multiple times).

I will leave this issue open until that pull request is merged. Once the pull request is merged we will put out a release so the fix is available through the pytket version available from pip. I'll let you know here once this is done.

[nquetschlich]

Hi @sjdilkes, thank you very much for your fast response. I am looking forward to that release and will check out the details of the PR.

[sjdilkes]

Hi @nquetschlich, #715 is now merged and pytket 1.11.0 is now available through pip with a fix for this issue.