layout_method and routing_method selectors in transpile() (#3999)

* add ability to select layout and routing method from top transpile function * set lookahead width/depth in increasing order * releasenote * review comments * lint * lint Co-authored-by: Kevin Krsulich <[email protected]>
Qiskit · Mar 30, 2020 · a8dcbe1 · a8dcbe1
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diff --git a/qiskit/compiler/transpile.py b/qiskit/compiler/transpile.py
@@ -13,6 +13,7 @@
 # that they have been altered from the originals.
 
 """Circuit transpile function"""
+import warnings
 from typing import List, Union, Dict, Callable, Any, Optional, Tuple
 from qiskit.circuit.quantumcircuit import QuantumCircuit
 from qiskit.providers import BaseBackend
@@ -40,6 +41,8 @@ def transpile(circuits: Union[QuantumCircuit, List[QuantumCircuit]],
               coupling_map: Optional[Union[CouplingMap, List[List[int]]]] = None,
               backend_properties: Optional[BackendProperties] = None,
               initial_layout: Optional[Union[Layout, Dict, List]] = None,
+              layout_method: Optional[str] = None,
+              routing_method: Optional[str] = None,
               seed_transpiler: Optional[int] = None,
               optimization_level: Optional[int] = None,
               pass_manager: Optional[PassManager] = None,
@@ -108,6 +111,10 @@ def transpile(circuits: Union[QuantumCircuit, List[QuantumCircuit]],
 
                     [qr[0], None, None, qr[1], None, qr[2]]
 
+        layout_method: Name of layout selection pass ('trivial', 'dense', 'noise_adaptive')
+            Sometimes a perfect layout can be available in which case the layout_method
+            may not run.
+        routing_method: Name of routing pass ('basic', 'lookahead', 'stochastic')
         seed_transpiler: Sets random seed for the stochastic parts of the transpiler
         optimization_level: How much optimization to perform on the circuits.
             Higher levels generate more optimized circuits,
@@ -170,6 +177,7 @@ def callback_func(**kwargs):
     circuits = circuits if isinstance(circuits, list) else [circuits]
     transpile_args = _parse_transpile_args(circuits, backend, basis_gates, coupling_map,
                                            backend_properties, initial_layout,
+                                           layout_method, routing_method,
                                            seed_transpiler, optimization_level,
                                            pass_manager, callback, output_name)
     # Check circuit width against number of qubits in coupling_map(s)
@@ -263,7 +271,8 @@ def _transpile_circuit(circuit_config_tuple: Tuple[QuantumCircuit, Dict]) -> Qua
 
 def _parse_transpile_args(circuits, backend,
                           basis_gates, coupling_map, backend_properties,
-                          initial_layout, seed_transpiler, optimization_level,
+                          initial_layout, layout_method, routing_method,
+                          seed_transpiler, optimization_level,
                           pass_manager, callback, output_name) -> List[Dict]:
     """Resolve the various types of args allowed to the transpile() function through
     duck typing, overriding args, etc. Refer to the transpile() docstring for details on
@@ -276,6 +285,9 @@ def _parse_transpile_args(circuits, backend,
     Returns:
         list[dicts]: a list of transpile parameters.
     """
+    if initial_layout is not None and layout_method is not None:
+        warnings.warn("initial_layout provided; layout_method is ignored.",
+                      UserWarning)
     # Each arg could be single or a list. If list, it must be the same size as
     # number of circuits. If single, duplicate to create a list of that size.
     num_circuits = len(circuits)
@@ -284,6 +296,8 @@ def _parse_transpile_args(circuits, backend,
     coupling_map = _parse_coupling_map(coupling_map, backend, num_circuits)
     backend_properties = _parse_backend_properties(backend_properties, backend, num_circuits)
     initial_layout = _parse_initial_layout(initial_layout, circuits)
+    layout_method = _parse_layout_method(layout_method, num_circuits)
+    routing_method = _parse_routing_method(routing_method, num_circuits)
     seed_transpiler = _parse_seed_transpiler(seed_transpiler, num_circuits)
     optimization_level = _parse_optimization_level(optimization_level, num_circuits)
     pass_manager = _parse_pass_manager(pass_manager, num_circuits)
@@ -292,17 +306,20 @@ def _parse_transpile_args(circuits, backend,
 
     list_transpile_args = []
     for args in zip(basis_gates, coupling_map, backend_properties,
-                    initial_layout, seed_transpiler, optimization_level,
+                    initial_layout, layout_method, routing_method,
+                    seed_transpiler, optimization_level,
                     pass_manager, output_name, callback):
         transpile_args = {'pass_manager_config': PassManagerConfig(basis_gates=args[0],
                                                                    coupling_map=args[1],
                                                                    backend_properties=args[2],
                                                                    initial_layout=args[3],
-                                                                   seed_transpiler=args[4]),
-                          'optimization_level': args[5],
-                          'pass_manager': args[6],
-                          'output_name': args[7],
-                          'callback': args[8]}
+                                                                   layout_method=args[4],
+                                                                   routing_method=args[5],
+                                                                   seed_transpiler=args[6]),
+                          'optimization_level': args[7],
+                          'pass_manager': args[8],
+                          'output_name': args[9],
+                          'callback': args[10]}
         list_transpile_args.append(transpile_args)
 
     return list_transpile_args
@@ -388,6 +405,18 @@ def _layout_from_raw(initial_layout, circuit):
     return initial_layout
 
 
+def _parse_layout_method(layout_method, num_circuits):
+    if not isinstance(layout_method, list):
+        layout_method = [layout_method] * num_circuits
+    return layout_method
+
+
+def _parse_routing_method(routing_method, num_circuits):
+    if not isinstance(routing_method, list):
+        routing_method = [routing_method] * num_circuits
+    return routing_method
+
+
 def _parse_seed_transpiler(seed_transpiler, num_circuits):
     if not isinstance(seed_transpiler, list):
         seed_transpiler = [seed_transpiler] * num_circuits

diff --git a/qiskit/transpiler/pass_manager_config.py b/qiskit/transpiler/pass_manager_config.py
@@ -2,7 +2,7 @@
 
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2017, 2019.
+# (C) Copyright IBM 2017, 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
@@ -17,24 +17,14 @@
 
 class PassManagerConfig:
     """Pass Manager Configuration.
-
-    Attributes:
-        initial_layout (Layout): Initial position of virtual qubits on physical
-            qubits.
-        basis_gates (list): List of basis gate names to unroll to.
-        coupling_map (CouplingMap): Directed graph represented a coupling map.
-        backend_properties (BackendProperties): Properties returned by a
-            backend, including
-            information on gate errors, readout errors, qubit coherence times,
-            etc.
-        seed_transpiler (int): Sets random seed for the stochastic parts of the
-            transpiler.
     """
 
     def __init__(self,
                  initial_layout=None,
                  basis_gates=None,
                  coupling_map=None,
+                 layout_method=None,
+                 routing_method=None,
                  backend_properties=None,
                  seed_transpiler=None):
         """Initialize a PassManagerConfig object
@@ -45,6 +35,10 @@ def __init__(self,
             basis_gates (list): List of basis gate names to unroll to.
             coupling_map (CouplingMap): Directed graph represented a coupling
                 map.
+            layout_method (str): the pass to use for choosing initial qubit
+                placement.
+            routing_method (str): the pass to use for routing qubits on the
+                architecture.
             backend_properties (BackendProperties): Properties returned by a
                 backend, including information on gate errors, readout errors,
                 qubit coherence times, etc.
@@ -54,5 +48,7 @@ def __init__(self,
         self.initial_layout = initial_layout
         self.basis_gates = basis_gates
         self.coupling_map = coupling_map
+        self.layout_method = layout_method
+        self.routing_method = routing_method
         self.backend_properties = backend_properties
         self.seed_transpiler = seed_transpiler
diff --git a/qiskit/transpiler/preset_passmanagers/level0.py b/qiskit/transpiler/preset_passmanagers/level0.py
@@ -26,14 +26,20 @@
 from qiskit.transpiler.passes import CXDirection
 from qiskit.transpiler.passes import SetLayout
 from qiskit.transpiler.passes import TrivialLayout
+from qiskit.transpiler.passes import DenseLayout
+from qiskit.transpiler.passes import NoiseAdaptiveLayout
 from qiskit.transpiler.passes import BarrierBeforeFinalMeasurements
+from qiskit.transpiler.passes import BasicSwap
+from qiskit.transpiler.passes import LookaheadSwap
 from qiskit.transpiler.passes import StochasticSwap
 from qiskit.transpiler.passes import FullAncillaAllocation
 from qiskit.transpiler.passes import EnlargeWithAncilla
 from qiskit.transpiler.passes import RemoveResetInZeroState
 from qiskit.transpiler.passes import ApplyLayout
 from qiskit.transpiler.passes import CheckCXDirection
 
+from qiskit.transpiler import TranspilerError
+
 
 def level_0_pass_manager(pass_manager_config: PassManagerConfig) -> PassManager:
     """Level 0 pass manager: no explicit optimization other than mapping to backend.
@@ -54,19 +60,32 @@ def level_0_pass_manager(pass_manager_config: PassManagerConfig) -> PassManager:
 
     Returns:
         a level 0 pass manager.
+
+    Raises:
+        TranspilerError: if the passmanager config is invalid.
     """
     basis_gates = pass_manager_config.basis_gates
     coupling_map = pass_manager_config.coupling_map
     initial_layout = pass_manager_config.initial_layout
+    layout_method = pass_manager_config.layout_method or 'trivial'
+    routing_method = pass_manager_config.routing_method or 'stochastic'
     seed_transpiler = pass_manager_config.seed_transpiler
+    backend_properties = pass_manager_config.backend_properties
 
-    # 1. Use trivial layout if no layout given
+    # 1. Choose an initial layout if not set by user (default: trivial layout)
     _given_layout = SetLayout(initial_layout)
 
     def _choose_layout_condition(property_set):
         return not property_set['layout']
 
-    _choose_layout = TrivialLayout(coupling_map)
+    if layout_method == 'trivial':
+        _choose_layout = TrivialLayout(coupling_map)
+    elif layout_method == 'dense':
+        _choose_layout = DenseLayout(coupling_map, backend_properties)
+    elif layout_method == 'noise_adaptive':
+        _choose_layout = NoiseAdaptiveLayout(backend_properties)
+    else:
+        raise TranspilerError("Invalid layout method %s." % layout_method)
 
     # 2. Extend dag/layout with ancillas using the full coupling map
     _embed = [FullAncillaAllocation(coupling_map), EnlargeWithAncilla(), ApplyLayout()]
@@ -80,8 +99,15 @@ def _choose_layout_condition(property_set):
     def _swap_condition(property_set):
         return not property_set['is_swap_mapped']
 
-    _swap = [BarrierBeforeFinalMeasurements(),
-             StochasticSwap(coupling_map, trials=20, seed=seed_transpiler)]
+    _swap = [BarrierBeforeFinalMeasurements()]
+    if routing_method == 'basic':
+        _swap += [BasicSwap(coupling_map)]
+    elif routing_method == 'stochastic':
+        _swap += [StochasticSwap(coupling_map, trials=20, seed=seed_transpiler)]
+    elif routing_method == 'lookahead':
+        _swap += [LookaheadSwap(coupling_map, search_depth=2, search_width=2)]
+    else:
+        raise TranspilerError("Invalid routing method %s." % routing_method)
 
     # 5. Unroll to the basis
     _unroll = Unroller(basis_gates)

diff --git a/qiskit/transpiler/preset_passmanagers/level1.py b/qiskit/transpiler/preset_passmanagers/level1.py
@@ -27,7 +27,11 @@
 from qiskit.transpiler.passes import CXDirection
 from qiskit.transpiler.passes import SetLayout
 from qiskit.transpiler.passes import TrivialLayout
+from qiskit.transpiler.passes import DenseLayout
+from qiskit.transpiler.passes import NoiseAdaptiveLayout
 from qiskit.transpiler.passes import BarrierBeforeFinalMeasurements
+from qiskit.transpiler.passes import BasicSwap
+from qiskit.transpiler.passes import LookaheadSwap
 from qiskit.transpiler.passes import StochasticSwap
 from qiskit.transpiler.passes import FullAncillaAllocation
 from qiskit.transpiler.passes import EnlargeWithAncilla
@@ -38,16 +42,18 @@
 from qiskit.transpiler.passes import ApplyLayout
 from qiskit.transpiler.passes import CheckCXDirection
 from qiskit.transpiler.passes import Layout2qDistance
-from qiskit.transpiler.passes import DenseLayout
+
+from qiskit.transpiler import TranspilerError
 
 
 def level_1_pass_manager(pass_manager_config: PassManagerConfig) -> PassManager:
     """Level 1 pass manager: light optimization by simple adjacent gate collapsing.
 
-    This pass manager applies the user-given initial layout. If none is given, and a trivial
-    layout (i-th virtual -> i-th physical) makes the circuit fit the coupling map, that is used.
-    Otherwise, the circuit is mapped to the most densely connected coupling subgraph, and swaps
-    are inserted to map. Any unused physical qubit is allocated as ancilla space.
+    This pass manager applies the user-given initial layout. If none is given,
+    and a trivial layout (i-th virtual -> i-th physical) makes the circuit fit
+    the coupling map, that is used.
+    Otherwise, the circuit is mapped to the most densely connected coupling subgraph,
+    and swaps are inserted to map. Any unused physical qubit is allocated as ancilla space.
     The pass manager then unrolls the circuit to the desired basis, and transforms the
     circuit to match the coupling map. Finally, optimizations in the form of adjacent
     gate collapse and redundant reset removal are performed.
@@ -61,10 +67,15 @@ def level_1_pass_manager(pass_manager_config: PassManagerConfig) -> PassManager:
 
     Returns:
         a level 1 pass manager.
+
+    Raises:
+        TranspilerError: if the passmanager config is invalid.
     """
     basis_gates = pass_manager_config.basis_gates
     coupling_map = pass_manager_config.coupling_map
     initial_layout = pass_manager_config.initial_layout
+    layout_method = pass_manager_config.layout_method or 'dense'
+    routing_method = pass_manager_config.routing_method or 'stochastic'
     seed_transpiler = pass_manager_config.seed_transpiler
     backend_properties = pass_manager_config.backend_properties
 
@@ -79,7 +90,14 @@ def _choose_layout_condition(property_set):
         return not property_set['layout']
 
     # 2. Use a better layout on densely connected qubits, if circuit needs swaps
-    _improve_layout = DenseLayout(coupling_map, backend_properties)
+    if layout_method == 'trivial':
+        _improve_layout = TrivialLayout(coupling_map)
+    elif layout_method == 'dense':
+        _improve_layout = DenseLayout(coupling_map, backend_properties)
+    elif layout_method == 'noise_adaptive':
+        _improve_layout = NoiseAdaptiveLayout(backend_properties)
+    else:
+        raise TranspilerError("Invalid layout method %s." % layout_method)
 
     def _not_perfect_yet(property_set):
         return property_set['trivial_layout_score'] is not None and \
@@ -97,8 +115,15 @@ def _not_perfect_yet(property_set):
     def _swap_condition(property_set):
         return not property_set['is_swap_mapped']
 
-    _swap = [BarrierBeforeFinalMeasurements(),
-             StochasticSwap(coupling_map, trials=20, seed=seed_transpiler)]
+    _swap = [BarrierBeforeFinalMeasurements()]
+    if routing_method == 'basic':
+        _swap += [BasicSwap(coupling_map)]
+    elif routing_method == 'stochastic':
+        _swap += [StochasticSwap(coupling_map, trials=50, seed=seed_transpiler)]
+    elif routing_method == 'lookahead':
+        _swap += [LookaheadSwap(coupling_map, search_depth=4, search_width=4)]
+    else:
+        raise TranspilerError("Invalid routing method %s." % routing_method)
 
     # 6. Unroll to the basis
     _unroll = Unroller(basis_gates)

diff --git a/qiskit/transpiler/preset_passmanagers/level2.py b/qiskit/transpiler/preset_passmanagers/level2.py
@@ -26,9 +26,13 @@
 from qiskit.transpiler.passes import CheckMap
 from qiskit.transpiler.passes import CXDirection
 from qiskit.transpiler.passes import SetLayout
-from qiskit.transpiler.passes import DenseLayout
 from qiskit.transpiler.passes import CSPLayout
+from qiskit.transpiler.passes import TrivialLayout
+from qiskit.transpiler.passes import DenseLayout
+from qiskit.transpiler.passes import NoiseAdaptiveLayout
 from qiskit.transpiler.passes import BarrierBeforeFinalMeasurements
+from qiskit.transpiler.passes import BasicSwap
+from qiskit.transpiler.passes import LookaheadSwap
 from qiskit.transpiler.passes import StochasticSwap
 from qiskit.transpiler.passes import FullAncillaAllocation
 from qiskit.transpiler.passes import EnlargeWithAncilla
@@ -40,6 +44,8 @@
 from qiskit.transpiler.passes import ApplyLayout
 from qiskit.transpiler.passes import CheckCXDirection
 
+from qiskit.transpiler import TranspilerError
+
 
 def level_2_pass_manager(pass_manager_config: PassManagerConfig) -> PassManager:
     """Level 2 pass manager: medium optimization by initial layout selection and
@@ -64,10 +70,15 @@ def level_2_pass_manager(pass_manager_config: PassManagerConfig) -> PassManager:
 
     Returns:
         a level 2 pass manager.
+
+    Raises:
+        TranspilerError: if the passmanager config is invalid.
     """
     basis_gates = pass_manager_config.basis_gates
     coupling_map = pass_manager_config.coupling_map
     initial_layout = pass_manager_config.initial_layout
+    layout_method = pass_manager_config.layout_method or 'dense'
+    routing_method = pass_manager_config.routing_method or 'stochastic'
     seed_transpiler = pass_manager_config.seed_transpiler
     backend_properties = pass_manager_config.backend_properties
 
@@ -78,7 +89,14 @@ def _choose_layout_condition(property_set):
         return not property_set['layout']
 
     _choose_layout_1 = CSPLayout(coupling_map, call_limit=1000, time_limit=10)
-    _choose_layout_2 = DenseLayout(coupling_map, backend_properties)
+    if layout_method == 'trivial':
+        _choose_layout_2 = TrivialLayout(coupling_map)
+    elif layout_method == 'dense':
+        _choose_layout_2 = DenseLayout(coupling_map, backend_properties)
+    elif layout_method == 'noise_adaptive':
+        _choose_layout_2 = NoiseAdaptiveLayout(backend_properties)
+    else:
+        raise TranspilerError("Invalid layout method %s." % layout_method)
 
     # 2. Extend dag/layout with ancillas using the full coupling map
     _embed = [FullAncillaAllocation(coupling_map), EnlargeWithAncilla(), ApplyLayout()]
@@ -92,8 +110,15 @@ def _choose_layout_condition(property_set):
     def _swap_condition(property_set):
         return not property_set['is_swap_mapped']
 
-    _swap = [BarrierBeforeFinalMeasurements(),
-             StochasticSwap(coupling_map, trials=20, seed=seed_transpiler)]
+    _swap = [BarrierBeforeFinalMeasurements()]
+    if routing_method == 'basic':
+        _swap += [BasicSwap(coupling_map)]
+    elif routing_method == 'stochastic':
+        _swap += [StochasticSwap(coupling_map, trials=100, seed=seed_transpiler)]
+    elif routing_method == 'lookahead':
+        _swap += [LookaheadSwap(coupling_map, search_depth=5, search_width=5)]
+    else:
+        raise TranspilerError("Invalid routing method %s." % routing_method)
 
     # 5. Unroll to the basis
     _unroll = Unroller(basis_gates)