Expand backend specific default methods to cover all stages

This commit expands the optional backend interface methods for
specifying an alternative default plugin for a transpiler stage to cover
all the stages in the preset pass manager. Originally this interface was
introduced in Qiskit#8648 for the translation and scheduling stages. This was
just a starting point as these were two stages most likely to require
backend specific compilation. However, since then this interface has
proven a useful tool for backend implementations but it's utility has
been limited to just translation and scheduling. There is a potential
role for a backend to provide an alternative default for the other
stages of the preset pass manager. This finishes what Qiskit#8648 starts by
expanding the interface to cover all the stages.

Author: mtreinish

qiskit/compiler/transpiler.py

@@ -277,6 +277,14 @@ def callback_func(**kwargs):
             scheduling_method = backend.get_scheduling_stage_plugin()
         if translation_method is None and hasattr(backend, "get_translation_stage_plugin"):
             translation_method = backend.get_translation_stage_plugin()
+        if init_method is None and hasattr(backend, "get_init_stage_plugin"):
+            init_method = backend.get_init_stage_plugin()
+        if layout_method is None and hasattr(backend, "get_layout_stage_plugin"):
+            layout_method = backend.get_layout_stage_plugin()
+        if routing_method is None and hasattr(backend, "get_routing_stage_plugin"):
+            routing_method = backend.get_routing_stage_plugin()
+        if optimization_method is None and hasattr(backend, "get_optimization_stage_plugin"):
+            optimization_method = backend.get_optimization_stage_plugin()
 
     output_name = _parse_output_name(output_name, circuits)
     coupling_map = _parse_coupling_map(coupling_map)

qiskit/providers/backend.py

@@ -51,23 +51,26 @@ class BackendV2(Backend, ABC):
     something like a ``shots`` field for a backend that runs experiments which
     would contain an int for how many shots to execute.
 
-    A backend object can optionally contain methods named
-    ``get_translation_stage_plugin`` and ``get_scheduling_stage_plugin``. If these
-    methods are present on a backend object and this object is used for
+    A backend object can optionally contain methods named:
+     * ``get_init_stage_plugin``
+     * ``get_layout_stage_plugin``
+     * ``get_routing_stage_plugin``
+     * ``get_translation_stage_plugin``
+     * ``get_scheduling_stage_plugin``.
+    If these methods are present on a backend object and this object is used for
     :func:`~.transpile` or :func:`~.generate_preset_pass_manager` the
     transpilation process will default to using the output from those methods
-    as the scheduling stage and the translation compilation stage. This
-    enables a backend which has custom requirements for compilation to specify a
-    stage plugin for these stages to enable custom transformation of
-    the circuit to ensure it is runnable on the backend. These hooks are enabled
-    by default and should only be used to enable extra compilation steps
-    if they are **required** to ensure a circuit is executable on the backend or
-    have the expected level of performance. These methods are passed no input
-    arguments and are expected to return a ``str`` representing the method name
-    which should be a stage plugin (see: :mod:`qiskit.transpiler.preset_passmanagers.plugin`
-    for more details on plugins). The typical expected use case is for a backend
-    provider to implement a stage plugin for ``translation`` or ``scheduling``
-    that contains the custom compilation passes and then for the hook methods on
+    as the respective compilation stage. This enables a backend which has custom
+    requirements or bespoke methods for compilation to specify a stage plugin for
+    these stages to enable custom compilation of the circuit to ensure it is
+    runnable on the backend. These hooks are enabled by default and should only
+    be used to enable extra compilation steps if they are **required** to ensure
+    a circuit is executable on the backend or have the expected level of performance.
+    These methods are passed no input arguments and are expected to return a ``str``
+    representing the method name which should be a stage plugin (see:
+    :mod:`qiskit.transpiler.preset_passmanagers.plugin` for more details on plugins).
+    The typical expected use case is for a backend provider to implement a stage
+    plugin that contains the custom compilation passes and then for the hook methods on
     the backend object to return the plugin name so that :func:`~.transpile` will
     use it by default when targeting the backend.
 

qiskit/transpiler/passmanager_config.py

@@ -138,10 +138,11 @@ def from_backend(cls, backend, _skip_target=False, **pass_manager_options):
             res.instruction_durations = backend.instruction_durations
         if res.target is None and not _skip_target:
             res.target = backend.target
-        if res.scheduling_method is None and hasattr(backend, "get_scheduling_stage_plugin"):
-            res.scheduling_method = backend.get_scheduling_stage_plugin()
-        if res.translation_method is None and hasattr(backend, "get_translation_stage_plugin"):
-            res.translation_method = backend.get_translation_stage_plugin()
+        stages = ["init", "layout", "routing", "translation", "optimization", "scheduling"]
+        for stage in stages:
+            if getattr(res, f"{stage}_method", None) is None:
+                if plugin_meth := getattr(backend, f"get_{stage}_stage_plugin", None):
+                    setattr(res, f"{stage}_method", plugin_meth())
         return res
 
     def __str__(self):

releasenotes/notes/expand_plugins_backend-e731bba7ef87ad2f.yaml

@@ -0,0 +1,11 @@
+---
+features_providers:
+  - Implementations of the :class:`.BackendV2` abstract class can now define the optional
+    methods ``get_init_stage_plugin``, ``get_layout_stage_plugin``,
+    ``get_routing_stage_plugin``, and ``get_optimization_stage_plugin`` which can be used
+    to specify alternative default plugins to use when invoking the transpiler for that
+    backend. When defined these methods should return the name of the plugin
+    to use by default when running the corresponding :ref:`transpiler-preset` stages when
+    targeting this backend object. These methods work in the same as the existing :class:`.BackendV2` methods
+    ``get_translation_stage_plugin`` and ``get_scheduling_stage_plugin`` but for the other
+    stages of the :ref:`transpiler-preset`.

test/python/transpiler/test_preset_passmanagers.py

@@ -44,6 +44,10 @@
     ALAPScheduleAnalysis,
     PadDynamicalDecoupling,
     RemoveResetInZeroState,
+    RemoveIdentityEquivalent,
+    TrivialLayout,
+    BasicSwap,
+    Optimize1qGates,
 )
 from qiskit.providers.fake_provider import GenericBackendV2
 from qiskit.converters import circuit_to_dag
@@ -81,13 +85,25 @@ def mock_get_passmanager_stage(
         )
         return pm
     elif stage_name == "init":
-        return PassManager([])
+        if plugin_name == "custom_stage_for_test":
+            return PassManager([RemoveIdentityEquivalent()])
+        else:
+            return PassManager([])
     elif stage_name == "routing":
-        return PassManager([])
+        if plugin_name == "custom_stage_for_test":
+            return PassManager([BasicSwap(pm_config.coupling_map)])
+        else:
+            return PassManager([])
     elif stage_name == "optimization":
-        return OptimizationPassManager().pass_manager(pm_config, optimization_level)
+        if plugin_name == "custom_stage_for_test":
+            return PassManager([Optimize1qGates()])
+        else:
+            return OptimizationPassManager().pass_manager(pm_config, optimization_level)
     elif stage_name == "layout":
-        return PassManager([])
+        if plugin_name == "custom_stage_for_test":
+            return PassManager([TrivialLayout(pm_config.coupling_map)])
+        else:
+            return PassManager([])
     else:
         raise RuntimeError("Failure, unexpected stage plugin combo for test")
 
@@ -1381,13 +1397,39 @@ def get_translation_stage_plugin(self):
                 """Custom post translation stage."""
                 return "custom_stage_for_test"
 
+            def get_init_stage_plugin(self):
+                """Custom init stage."""
+                return "custom_stage_for_test"
+
+            def get_layout_stage_plugin(self):
+                """Custom layout stage."""
+                return "custom_stage_for_test"
+
+            def get_routing_stage_plugin(self):
+                """Custom routing stage."""
+                return "custom_stage_for_test"
+
+            def get_optimization_stage_plugin(self):
+                """Custom optimization stage."""
+                return "custom_stage_for_test"
+
         target = TargetBackend(num_qubits=7, coupling_map=LAGOS_CMAP, seed=42)
         pm = generate_preset_pass_manager(optimization_level, backend=target)
         self.assertIsInstance(pm, PassManager)
 
         pass_list = [x.__class__.__name__ for x in pm.to_flow_controller().tasks]
-        self.assertIn("PadDynamicalDecoupling", pass_list)
-        self.assertIn("ALAPScheduleAnalysis", pass_list)
+        expected = [
+            "ContainsInstruction",
+            "ConditionalController",
+            "RemoveIdentityEquivalent",
+            "TrivialLayout",
+            "BasicSwap",
+            "RemoveResetInZeroState",
+            "Optimize1qGates",
+            "ALAPScheduleAnalysis",
+            "PadDynamicalDecoupling",
+        ]
+        self.assertEqual(pass_list, expected)
         post_translation_pass_list = [
             x.__class__.__name__ for x in pm.translation.to_flow_controller().tasks
         ]