Change switch_to_new condition in TwoQubitCompilationTargetGateset to switch only when it's optimal in terms of 2q gate counts
#5405
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… switch only when it's optimal in terms of 2q gate counts
| any( | ||
| protocols.num_qubits(op) == 2 and op not in self | ||
| for op in ops.flatten_to_ops(old_optree) | ||
| ) |
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Can we do this part of the check before constructing new_optree so we don't waste time on it if it's not needed?
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We will have to construct the new_optree irrespective of whether this check returns a True or False.
We will not switch to the new_optree only if both the checks are false (i.e. all 2q operations in old_optree are in self and old_2q_gate_count <= new_2q_gate_count.
| return new_optree if switch_to_new else old_optree | ||
| if switch_to_new: | ||
| return new_optree | ||
| mapped_old_optree: List['cirq.OP_TREE'] = [] |
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This is different from the old behavior: if all old ops (1q or 2q) are in the target gateset and new_2q_gate_count >= old_2q_gate_count, this previously would have returned the old optree. Is this intended?
(If gateset behavior would prevent this case from occurring, a comment explaining this would be helpful)
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this previously would have returned the old optree.
The behavior is unchanged, i.e., if all old ops (1q or 2q) are in the target gateset and new_2q_gate_count >= old_2q_gate_count; it would have previously returned old_optree and it would still return old_optree.
Notice that the mapped_old_optree will be same as old_optree if all operations are in self (the first if condition in the loop below).
… switch only when it's optimal in terms of 2q gate counts (quantumlib#5405)
… switch only when it's optimal in terms of 2q gate counts (quantumlib#5405)
… switch only when it's optimal in terms of 2q gate counts (quantumlib#5405)
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cirq.TwoQubitCompilationTargetGatesetcurrently implements a logic to compare the analytical decomposition of a merged 2q connected component (new_optree) with the one which already exists in the circuit (old_optree) and switch iff:old_optreeis not part of the target gatesetnew_optreeis less than those inold_optreeThis PR changes the switch condition to:
old_optreeis not part of the target gateset # Any ==> Any 2qnew_optreeis less than those inold_optreeThis is useful because if the old merged connected component (i.e.
old_optree) is optimal in terms of 2q gates but contains single qubit gates outside of the target gateset; we should only replace the single qubit gates and not the entire decomposition with a more in-efficient decomposition.See the newly added test for a dummy example.
cc @verult ; Part of #5254