new unroll for-loops transpilation pass

qiskit/transpiler/passes/optimization/unroll_forloops.py

@@ -0,0 +1,43 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2023.
+#
+# 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
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""TODO"""
+from qiskit.circuit import ForLoopOp
+from qiskit.transpiler.basepasses import TransformationPass
+from qiskit.transpiler.passes.utils import control_flow
+from qiskit.converters import circuit_to_dag
+
+
+class UnrollForLoops(TransformationPass):
+    """TODO"""
+
+    @control_flow.trivial_recurse
+    def run(self, dag):
+        """Run the UnrollForLoops pass on `dag`.
+
+        Args:
+            dag (DAGCircuit): the directed acyclic graph to run on.
+
+        Returns:
+            DAGCircuit: Transformed DAG.
+        """
+        for forloop_op in dag.op_nodes(ForLoopOp):
+            (indexset, loop_parameter, body) = forloop_op.op.params
+            # TODO do not unroll when break_loop inside body
+
+            unrolled_dag = circuit_to_dag(body).copy_empty_like()
+            for index_value in indexset:
+                bound_body_dag = circuit_to_dag(body.bind_parameters({loop_parameter: index_value}))
+                unrolled_dag.compose(bound_body_dag, inplace=True)
+            dag.substitute_node_with_dag(forloop_op, unrolled_dag)
+
+        return dag

test/python/transpiler/test_unroll_forloops.py

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+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2023.
+#
+# 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
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""Test the unroll_forloops pass"""
+
+import unittest
+
+from qiskit.circuit import QuantumCircuit, Parameter, QuantumRegister, ClassicalRegister
+from qiskit.transpiler import PassManager
+from qiskit.test import QiskitTestCase
+from qiskit.transpiler.passes.optimization.unroll_forloops import UnrollForLoops
+
+
+class TestUnrool(QiskitTestCase):
+    """Test UnrollForLoops pass"""
+
+    def test_range(self):
+        """TODO"""
+        qreg, creg = QuantumRegister(5, "q"), ClassicalRegister(2, "c")
+
+        body = QuantumCircuit(3, 1)
+        loop_parameter = Parameter("foo")
+        indexset = range(0, 10, 2)
+
+        body.rx(loop_parameter, [0, 1, 2])
+
+        circuit = QuantumCircuit(qreg, creg)
+        circuit.for_loop(indexset, loop_parameter, body, [1, 2, 3], [1])
+
+        expected = QuantumCircuit(qreg, creg)
+        for index_loop in indexset:
+            expected.rx(index_loop, [1, 2, 3])
+
+        passmanager = PassManager()
+        passmanager.append(UnrollForLoops())
+        result = passmanager.run(circuit)
+
+        self.assertEqual(result, expected)
+
+
+if __name__ == "__main__":
+    unittest.main()