Source code for qiskit.transpiler.passes.scheduling.asap

# This code is part of Qiskit.
# (C) Copyright IBM 2020.
# 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
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"""ASAP Scheduling."""

from qiskit.circuit import Delay, Qubit, Measure
from qiskit.dagcircuit import DAGCircuit
from qiskit.transpiler.exceptions import TranspilerError
from qiskit.utils.deprecation import deprecate_func

from .base_scheduler import BaseSchedulerTransform

[docs]class ASAPSchedule(BaseSchedulerTransform): """ASAP Scheduling pass, which schedules the start time of instructions as early as possible.. See :class:`~qiskit.transpiler.passes.scheduling.base_scheduler.BaseSchedulerTransform` for the detailed behavior of the control flow operation, i.e. ``c_if``. .. note:: This base class has been superseded by :class:`~.ASAPScheduleAnalysis` and the new scheduling workflow. It will be deprecated and subsequently removed in a future release. """ @deprecate_func( additional_msg=( "Instead, use :class:`~.ASAPScheduleAnalysis`, which is an " "analysis pass that requires a padding pass to later modify the circuit." ), since="0.21.0", pending=True, ) def __init__(self, *args, **kwargs): super().__init__(*args, **kwargs)
[docs] def run(self, dag): """Run the ASAPSchedule pass on `dag`. Args: dag (DAGCircuit): DAG to schedule. Returns: DAGCircuit: A scheduled DAG. Raises: TranspilerError: if the circuit is not mapped on physical qubits. TranspilerError: if conditional bit is added to non-supported instruction. """ if len(dag.qregs) != 1 or dag.qregs.get("q", None) is None: raise TranspilerError("ASAP schedule runs on physical circuits only") time_unit = self.property_set["time_unit"] new_dag = DAGCircuit() for qreg in dag.qregs.values(): new_dag.add_qreg(qreg) for creg in dag.cregs.values(): new_dag.add_creg(creg) idle_after = {q: 0 for q in dag.qubits + dag.clbits} bit_indices = {q: index for index, q in enumerate(dag.qubits)} for node in dag.topological_op_nodes(): op_duration = self._get_node_duration(node, bit_indices, dag) # compute t0, t1: instruction interval, note that # t0: start time of instruction # t1: end time of instruction if isinstance(node.op, self.CONDITIONAL_SUPPORTED): t0q = max(idle_after[q] for q in node.qargs) if node.op.condition_bits: # conditional is bit tricky due to conditional_latency t0c = max(idle_after[bit] for bit in node.op.condition_bits) if t0q > t0c: # This is situation something like below # # |t0q # Q ▒▒▒▒▒▒▒▒▒░░ # C ▒▒▒░░░░░░░░ # |t0c # # In this case, you can insert readout access before tq0 # # |t0q # Q ▒▒▒▒▒▒▒▒▒▒▒ # C ▒▒▒░░░▒▒░░░ # |t0q - conditional_latency # t0c = max(t0q - self.conditional_latency, t0c) t1c = t0c + self.conditional_latency for bit in node.op.condition_bits: # Lock clbit until state is read idle_after[bit] = t1c # It starts after register read access t0 = max(t0q, t1c) else: t0 = t0q t1 = t0 + op_duration else: if node.op.condition_bits: raise TranspilerError( f"Conditional instruction {} is not supported in ASAP scheduler." ) if isinstance(node.op, Measure): # measure instruction handling is bit tricky due to clbit_write_latency t0q = max(idle_after[q] for q in node.qargs) t0c = max(idle_after[c] for c in node.cargs) # Assume following case (t0c > t0q) # # |t0q # Q ▒▒▒▒░░░░░░░░░░░░ # C ▒▒▒▒▒▒▒▒░░░░░░░░ # |t0c # # In this case, there is no actual clbit access until clbit_write_latency. # The node t0 can be push backward by this amount. # # |t0q' = t0c - clbit_write_latency # Q ▒▒▒▒░░▒▒▒▒▒▒▒▒▒▒ # C ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ # |t0c' = t0c # # rather than naively doing # # |t0q' = t0c # Q ▒▒▒▒░░░░▒▒▒▒▒▒▒▒ # C ▒▒▒▒▒▒▒▒░░░▒▒▒▒▒ # |t0c' = t0c + clbit_write_latency # t0 = max(t0q, t0c - self.clbit_write_latency) t1 = t0 + op_duration for clbit in node.cargs: idle_after[clbit] = t1 else: # It happens to be directives such as barrier t0 = max(idle_after[bit] for bit in node.qargs + node.cargs) t1 = t0 + op_duration # Add delay to qubit wire for bit in node.qargs: delta = t0 - idle_after[bit] if delta > 0 and isinstance(bit, Qubit) and self._delay_supported(bit_indices[bit]): new_dag.apply_operation_back(Delay(delta, time_unit), [bit], []) idle_after[bit] = t1 new_dag.apply_operation_back(node.op, node.qargs, node.cargs) circuit_duration = max(idle_after.values()) for bit, after in idle_after.items(): delta = circuit_duration - after if not (delta > 0 and isinstance(bit, Qubit)): continue if self._delay_supported(bit_indices[bit]): new_dag.apply_operation_back(Delay(delta, time_unit), [bit], []) = new_dag.metadata = dag.metadata new_dag.calibrations = dag.calibrations # set circuit duration and unit to indicate it is scheduled new_dag.duration = circuit_duration new_dag.unit = time_unit return new_dag