Allow circuits w/ control flow in O2 and O3 (Qiskit#10372)

* Allow control flow in opt levels 2 and 3.

* Add release note.

* Enable testing for opt 2 and 3.

* Remove guard on translation_method='synthesis'.

* Fix test for synthesis guard.

* Skip o3 qpy full path transpile test on windows

In CI we're seeing a reliable failure on windows when scipy is calling
LAPACK. This appears to be unrelated to the change in this PR branch and
is isolated to specific windows environments. This commit adds a skip
condition to skip that one test to workaround the failure in CI. The
wider issue with scipy compatibility on windows is being tracked in
issue Qiskit#10345, when we have a conclusion to that and can reliably run
this test we should remove this skip condition.

---------

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

qiskit/transpiler/preset_passmanagers/common.py

@@ -66,11 +66,9 @@
     "routing_method": _ControlFlowState(
         working={"none", "stochastic", "sabre"}, not_working={"lookahead", "basic"}
     ),
-    # 'synthesis' is not a supported translation method because of the block-collection passes
-    # involved; we currently don't have a neat way to pass the information about nested blocks - the
-    # `UnitarySynthesis` pass itself is control-flow aware.
     "translation_method": _ControlFlowState(
-        working={"translator", "unroller"}, not_working={"synthesis"}
+        working={"translator", "synthesis", "unroller"},
+        not_working=set(),
     ),
     "optimization_method": _ControlFlowState(working=set(), not_working=set()),
     "scheduling_method": _ControlFlowState(working=set(), not_working={"alap", "asap"}),

qiskit/transpiler/preset_passmanagers/level2.py

@@ -254,8 +254,14 @@ def _unroll_condition(property_set):
         sched = plugin_manager.get_passmanager_stage(
             "scheduling", scheduling_method, pass_manager_config, optimization_level=2
         )
-    init = common.generate_error_on_control_flow(
-        "The optimizations in optimization_level=2 do not yet support control flow."
+    init = common.generate_control_flow_options_check(
+        layout_method=layout_method,
+        routing_method=routing_method,
+        translation_method=translation_method,
+        optimization_method=optimization_method,
+        scheduling_method=scheduling_method,
+        basis_gates=basis_gates,
+        target=target,
     )
     if init_method is not None:
         init += plugin_manager.get_passmanager_stage(

qiskit/transpiler/preset_passmanagers/level3.py

@@ -189,8 +189,14 @@ def _opt_control(property_set):
     ]
 
     # Build pass manager
-    init = common.generate_error_on_control_flow(
-        "The optimizations in optimization_level=3 do not yet support control flow."
+    init = common.generate_control_flow_options_check(
+        layout_method=layout_method,
+        routing_method=routing_method,
+        translation_method=translation_method,
+        optimization_method=optimization_method,
+        scheduling_method=scheduling_method,
+        basis_gates=basis_gates,
+        target=target,
     )
     if init_method is not None:
         init += plugin_manager.get_passmanager_stage(

releasenotes/notes/ctrl-flow-o2-o3-83f660d704226848.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Control-flow operations are now supported through the transpiler at
+    all optimization levels, including levels 2 and 3 (e.g. calling
+    :func:`.transpile` or :func:`.generate_preset_pass_manager` with
+    keyword argument ``optimization_level=3``).

test/python/compiler/test_transpiler.py

@@ -1525,9 +1525,7 @@ def test_target_ideal_gates(self, opt_level):
 
         self.assertEqual(Operator.from_circuit(result), Operator.from_circuit(qc))
 
-    # TODO: Add optimization level 2 and 3 after they support control flow
-    # compilation
-    @data(0, 1)
+    @data(0, 1, 2, 3)
     def test_transpile_with_custom_control_flow_target(self, opt_level):
         """Test transpile() with a target and constrol flow ops."""
         target = FakeMumbaiV2().target
@@ -1759,10 +1757,15 @@ def test_qpy_roundtrip_backendv2(self, optimization_level):
 
         self.assertEqual(round_tripped, transpiled)
 
-    @data(0, 1)
+    @data(0, 1, 2, 3)
     def test_qpy_roundtrip_control_flow(self, optimization_level):
         """Test that the output of a transpiled circuit with control flow can be round-tripped
         through QPY."""
+        if optimization_level == 3 and sys.platform == "win32":
+            self.skipTest(
+                "This test case triggers a bug in the eigensolver routine on windows. "
+                "See #10345 for more details."
+            )
 
         backend = FakeMelbourne()
         transpiled = transpile(
@@ -1781,7 +1784,7 @@ def test_qpy_roundtrip_control_flow(self, optimization_level):
         round_tripped = qpy.load(buffer)[0]
         self.assertEqual(round_tripped, transpiled)
 
-    @data(0, 1)
+    @data(0, 1, 2, 3)
     def test_qpy_roundtrip_control_flow_backendv2(self, optimization_level):
         """Test that the output of a transpiled circuit with control flow can be round-tripped
         through QPY."""
@@ -1818,7 +1821,7 @@ def test_qasm3_output(self, optimization_level):
         # itself doesn't throw an error, though.
         self.assertIsInstance(qasm3.dumps(transpiled).strip(), str)
 
-    @data(0, 1)
+    @data(0, 1, 2, 3)
     def test_qasm3_output_control_flow(self, optimization_level):
         """Test that the output of a transpiled circuit with control flow can be dumped into
         OpenQASM 3."""

test/python/transpiler/test_preset_passmanagers.py

@@ -1427,7 +1427,7 @@ def get_translation_stage_plugin(self):
 class TestIntegrationControlFlow(QiskitTestCase):
     """Integration tests for control-flow circuits through the preset pass managers."""
 
-    @data(0, 1)
+    @data(0, 1, 2, 3)
     def test_default_compilation(self, optimization_level):
         """Test that a simple circuit with each type of control-flow passes a full transpilation
         pipeline with the defaults."""
@@ -1503,7 +1503,7 @@ def _visit_block(circuit, stack=None):
         # Assert routing ran.
         _visit_block(transpiled)
 
-    @data(0, 1)
+    @data(0, 1, 2, 3)
     def test_allow_overriding_defaults(self, optimization_level):
         """Test that the method options can be overridden."""
         circuit = QuantumCircuit(3, 1)
@@ -1541,7 +1541,7 @@ def callback(pass_, **_):
         self.assertNotIn("SabreLayout", calls)
         self.assertNotIn("BasisTranslator", calls)
 
-    @data(0, 1)
+    @data(0, 1, 2, 3)
     def test_invalid_methods_raise_on_control_flow(self, optimization_level):
         """Test that trying to use an invalid method with control flow fails."""
         qc = QuantumCircuit(1)
@@ -1550,22 +1550,10 @@ def test_invalid_methods_raise_on_control_flow(self, optimization_level):
 
         with self.assertRaisesRegex(TranspilerError, "Got routing_method="):
             transpile(qc, routing_method="lookahead", optimization_level=optimization_level)
-        with self.assertRaisesRegex(TranspilerError, "Got translation_method="):
-            transpile(qc, translation_method="synthesis", optimization_level=optimization_level)
         with self.assertRaisesRegex(TranspilerError, "Got scheduling_method="):
             transpile(qc, scheduling_method="alap", optimization_level=optimization_level)
 
-    @data(2, 3)
-    def test_unsupported_levels_raise(self, optimization_level):
-        """Test that trying to use an invalid method with control flow fails."""
-        qc = QuantumCircuit(1)
-        with qc.for_loop((1,)):
-            qc.x(0)
-
-        with self.assertRaisesRegex(TranspilerError, "The optimizations in optimization_level="):
-            transpile(qc, optimization_level=optimization_level)
-
-    @data(0, 1)
+    @data(0, 1, 2, 3)
     def test_unsupported_basis_gates_raise(self, optimization_level):
         """Test that trying to transpile a control-flow circuit for a backend that doesn't support
         the necessary operations in its `basis_gates` will raise a sensible error."""
@@ -1591,7 +1579,7 @@ def test_unsupported_basis_gates_raise(self, optimization_level):
         with self.assertRaisesRegex(TranspilerError, "The control-flow construct.*not supported"):
             transpile(qc, backend, optimization_level=optimization_level)
 
-    @data(0, 1)
+    @data(0, 1, 2, 3)
     def test_unsupported_targets_raise(self, optimization_level):
         """Test that trying to transpile a control-flow circuit for a backend that doesn't support
         the necessary operations in its `Target` will raise a more sensible error."""