Code source de qiskit.transpiler.passes.scheduling.scheduling.alap

# 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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"""ALAP Scheduling."""
from qiskit.circuit import Measure
from qiskit.transpiler.exceptions import TranspilerError

from qiskit.transpiler.passes.scheduling.scheduling.base_scheduler import BaseScheduler

[docs]class ALAPScheduleAnalysis(BaseScheduler): """ALAP Scheduling pass, which schedules the **stop** time of instructions as late as possible. See the :ref:`scheduling_stage` section in the :mod:`qiskit.transpiler` module documentation for the detailed behavior of the control flow operation, i.e. ``c_if``. """
[docs] def run(self, dag): """Run the ALAPSchedule 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("ALAP schedule runs on physical circuits only") conditional_latency = self.property_set.get("conditional_latency", 0) clbit_write_latency = self.property_set.get("clbit_write_latency", 0) node_start_time = {} idle_before = {q: 0 for q in dag.qubits + dag.clbits} for node in reversed(list(dag.topological_op_nodes())): op_duration = self._get_node_duration(node, dag) # compute t0, t1: instruction interval, note that # t0: start time of instruction # t1: end time of instruction # since this is alap scheduling, node is scheduled in reversed topological ordering # and nodes are packed from the very end of the circuit. # the physical meaning of t0 and t1 is flipped here. if isinstance(node.op, self.CONDITIONAL_SUPPORTED): t0q = max(idle_before[q] for q in node.qargs) if node.op.condition_bits: # conditional is bit tricky due to conditional_latency t0c = max(idle_before[c] for c in node.op.condition_bits) # Assume following case (t0c > t0q): # # |t0q # Q β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–’β–’β–’ # C β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–’β–’β–’β–’β–’β–’β–’β–’ # |t0c # # In this case, there is no actual clbit read before gate. # # |t0q' = t0c - conditional_latency # Q β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–’β–’β–’β–‘β–‘β–’β–’β–’ # C β–‘β–‘β–‘β–‘β–‘β–‘β–’β–’β–’β–’β–’β–’β–’β–’β–’β–’ # |t1c' = t0c + conditional_latency # # rather than naively doing # # |t1q' = t0c + duration # Q β–‘β–‘β–‘β–‘β–‘β–’β–’β–’β–‘β–‘β–‘β–‘β–‘β–’β–’β–’ # C β–‘β–‘β–’β–’β–‘β–‘β–‘β–‘β–’β–’β–’β–’β–’β–’β–’β–’ # |t1c' = t0c + duration + conditional_latency # t0 = max(t0q, t0c - op_duration) t1 = t0 + op_duration for clbit in node.op.condition_bits: idle_before[clbit] = t1 + conditional_latency else: t0 = t0q t1 = t0 + op_duration else: if node.op.condition_bits: raise TranspilerError( f"Conditional instruction {} is not supported in ALAP scheduler." ) if isinstance(node.op, Measure): # clbit time is always right (alap) justified t0 = max(idle_before[bit] for bit in node.qargs + node.cargs) t1 = t0 + op_duration # # |t1 = t0 + duration # Q β–‘β–‘β–‘β–‘β–‘β–’β–’β–’β–’β–’β–’β–’β–’β–’β–’β–’ # C β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–‘β–’β–’β–’β–’β–’β–’β–’ # |t0 + (duration - clbit_write_latency) # for clbit in node.cargs: idle_before[clbit] = t0 + (op_duration - clbit_write_latency) else: # It happens to be directives such as barrier t0 = max(idle_before[bit] for bit in node.qargs + node.cargs) t1 = t0 + op_duration for bit in node.qargs: idle_before[bit] = t1 node_start_time[node] = t1 # Compute maximum instruction available time, i.e. very end of t1 circuit_duration = max(idle_before.values()) # Note that ALAP pass is inversely schedule, thus # t0 is computed by subtracting entire circuit duration from t1. self.property_set["node_start_time"] = { n: circuit_duration - t1 for n, t1 in node_start_time.items() }