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unroll_3q_or_more.py
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unroll_3q_or_more.py
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# This code is part of Qiskit.
#
# (C) Copyright IBM 2017, 2018.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.
"""Recursively expands 3q+ gates until the circuit only contains 2q or 1q gates."""
from qiskit.transpiler.basepasses import TransformationPass
from qiskit.transpiler.passes.utils import control_flow
from qiskit.exceptions import QiskitError
from qiskit.circuit import ControlFlowOp
from qiskit.converters.circuit_to_dag import circuit_to_dag
class Unroll3qOrMore(TransformationPass):
"""Recursively expands 3q+ gates until the circuit only contains 2q or 1q gates."""
def __init__(self, target=None, basis_gates=None):
"""Initialize the Unroll3qOrMore pass
Args:
target (Target): The target object representing the compilation
target. If specified any multi-qubit instructions in the
circuit when the pass is run that are supported by the target
device will be left in place. If both this and ``basis_gates``
are specified only the target will be checked.
basis_gates (list): A list of basis gate names that the target
device supports. If specified any gate names in the circuit
which are present in this list will not be unrolled. If both
this and ``target`` are specified only the target will be used
for checking which gates are supported.
"""
super().__init__()
self.target = target
self.basis_gates = None
if basis_gates is not None:
self.basis_gates = set(basis_gates)
def run(self, dag):
"""Run the Unroll3qOrMore pass on `dag`.
Args:
dag(DAGCircuit): input dag
Returns:
DAGCircuit: output dag with maximum node degrees of 2
Raises:
QiskitError: if a 3q+ gate is not decomposable
"""
for node in dag.multi_qubit_ops():
if dag.has_calibration_for(node):
continue
if isinstance(node.op, ControlFlowOp):
node.op = control_flow.map_blocks(self.run, node.op)
continue
if self.target is not None:
# Treat target instructions as global since this pass can be run
# prior to layout and routing we don't have physical qubits from
# the circuit yet
if node.name in self.target:
continue
elif self.basis_gates is not None and node.name in self.basis_gates:
continue
# TODO: allow choosing other possible decompositions
rule = node.op.definition.data
if not rule:
if rule == []: # empty node
dag.remove_op_node(node)
continue
raise QiskitError(
"Cannot unroll all 3q or more gates. "
"No rule to expand instruction %s." % node.op.name
)
decomposition = circuit_to_dag(node.op.definition, copy_operations=False)
decomposition = self.run(decomposition) # recursively unroll
dag.substitute_node_with_dag(node, decomposition)
return dag