Avoid routing 2q barriers in SabreSwap #11295
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This commit fixes an oversight in the sabre swap pass where a 2 qubit barrier would have been treated like a 2 qubit gate and swaps could potentially be inserted if the sabre algorithm thought it didn't have connectivity for the qargs to the barrier. However as barrier is just a compiler directive it is valid on all qubit pairs so this swap insertion was unnecessary, it was still valid but just not an optimal output. This commit fixes it by adding context to the sabre dag around whether a given node is a directive (and valid on all qubits) or not.
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I believe you also need to update extended set population to ignore directives:
if required_predecessors[successor_index] == 0 {
if !dag.dag[node].directive && !dag.node_blocks.contains_key(&successor_index) {
if let [a, b] = dag.dag[successor_node].qubits[..] {
extended_set.push([a.to_phys(layout), b.to_phys(layout)]);
}
}
to_visit.push(successor_node);
}Otherwise, this looks good!
Co-authored-by: Kevin Hartman <kevin@hart.mn>
Done in: 89da56e |
This commit updates a layout in the: `TestSabreLayout.test_layout_many_search_trials` test case which was recently changed in Qiskit#10323. The change in test ouput caused by Qiskit#10323 is what triggered the investigation into this bugfix and now that barriers are being treated correctly by sabre the layout doesn't change in the test case anymore and this is reverting the test assertion to use the original layout before Qiskit#10323 was merged.
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kevinhartman
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Nov 23, 2023
gluonhiggs
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Nov 23, 2023
* Avoid routing 2q barriers in SabreSwap This commit fixes an oversight in the sabre swap pass where a 2 qubit barrier would have been treated like a 2 qubit gate and swaps could potentially be inserted if the sabre algorithm thought it didn't have connectivity for the qargs to the barrier. However as barrier is just a compiler directive it is valid on all qubit pairs so this swap insertion was unnecessary, it was still valid but just not an optimal output. This commit fixes it by adding context to the sabre dag around whether a given node is a directive (and valid on all qubits) or not. * Update rust tests too * Skip directives in extended set generation too Co-authored-by: Kevin Hartman <kevin@hart.mn> * Add release note * Update test layout in test_layout_many_search_trials This commit updates a layout in the: `TestSabreLayout.test_layout_many_search_trials` test case which was recently changed in Qiskit#10323. The change in test ouput caused by Qiskit#10323 is what triggered the investigation into this bugfix and now that barriers are being treated correctly by sabre the layout doesn't change in the test case anymore and this is reverting the test assertion to use the original layout before Qiskit#10323 was merged. --------- Co-authored-by: Kevin Hartman <kevin@hart.mn>
FabianBrings
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to FabianBrings/qiskit
that referenced
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Nov 27, 2023
* Avoid routing 2q barriers in SabreSwap This commit fixes an oversight in the sabre swap pass where a 2 qubit barrier would have been treated like a 2 qubit gate and swaps could potentially be inserted if the sabre algorithm thought it didn't have connectivity for the qargs to the barrier. However as barrier is just a compiler directive it is valid on all qubit pairs so this swap insertion was unnecessary, it was still valid but just not an optimal output. This commit fixes it by adding context to the sabre dag around whether a given node is a directive (and valid on all qubits) or not. * Update rust tests too * Skip directives in extended set generation too Co-authored-by: Kevin Hartman <kevin@hart.mn> * Add release note * Update test layout in test_layout_many_search_trials This commit updates a layout in the: `TestSabreLayout.test_layout_many_search_trials` test case which was recently changed in Qiskit#10323. The change in test ouput caused by Qiskit#10323 is what triggered the investigation into this bugfix and now that barriers are being treated correctly by sabre the layout doesn't change in the test case anymore and this is reverting the test assertion to use the original layout before Qiskit#10323 was merged. --------- Co-authored-by: Kevin Hartman <kevin@hart.mn>
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Summary
This commit fixes an oversight in the sabre swap pass where a 2 qubit barrier would have been treated like a 2 qubit gate and swaps could potentially be inserted if the sabre algorithm thought it didn't have connectivity for the qargs to the barrier. However as barrier is just a compiler directive it is valid on all qubit pairs so this swap insertion was unnecessary, it was still valid but just not an optimal output. This commit fixes it by adding context to the sabre dag around whether a given node is a directive (and valid on all qubits) or not.
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