[CQT-266] Routing checker pass (#411)

* Added a Routing Checker pass

* Delete openosq12 directory (virtualenv)

* Added Routing Checker pass

* Fixed errors

* Fixed errors

* Fixed errors

* Fixed errors

* Implemented feedback

---------

Co-authored-by: Oancea <rares.oancea@tno.nl>
Co-authored-by: Chris Elenbaas <chris.elenbaas@tno.nl>

Author: 3 people

opensquirrel/circuit.py

@@ -10,6 +10,7 @@
     from opensquirrel.passes.decomposer import Decomposer
     from opensquirrel.passes.mapper import Mapper
     from opensquirrel.passes.merger.general_merger import Merger
+    from opensquirrel.passes.router.general_router import Router
     from opensquirrel.register_manager import RegisterManager
 
 
@@ -86,6 +87,10 @@ def qubit_register_name(self) -> str:
     def bit_register_name(self) -> str:
         return self.register_manager.get_bit_register_name()
 
+    def route(self, router: Router) -> None:
+        """Generic router pass. It applies the given Router to the circuit."""
+        router.route(self.ir)
+
     def merge(self, merger: Merger) -> None:
         """Generic merge pass. It applies the given merger to the circuit."""
         merger.merge(self.ir, self.qubit_register_size)

opensquirrel/passes/router/general_router.py

@@ -0,0 +1,9 @@
+from abc import ABC, abstractmethod
+
+from opensquirrel.ir import IR
+
+
+class Router(ABC):
+    @abstractmethod
+    def route(self, ir: IR) -> None:
+        raise NotImplementedError

opensquirrel/passes/router/routing_checker.py

@@ -0,0 +1,28 @@
+from typing import cast
+
+from opensquirrel.ir import IR, Instruction, Qubit
+from opensquirrel.passes.router.general_router import Router
+
+
+class RoutingChecker(Router):
+    def __init__(self, backend_connectivity_diagram: dict[int, list[int]]) -> None:
+        self.backend_connectivity_diagram = backend_connectivity_diagram
+
+    def route(self, ir: IR) -> None:
+        non_executable_interactions = []
+        for statement in ir.statements:
+            instruction: Instruction = cast(Instruction, statement)
+            args = instruction.arguments
+            if args and len(args) > 1 and all(isinstance(arg, Qubit) for arg in args):
+                qubit_args = [arg for arg in args if isinstance(arg, Qubit)]
+                qubit_index_pairs = [(q0.index, q1.index) for q0, q1 in zip(qubit_args[:-1], qubit_args[1:])]
+                for i, j in qubit_index_pairs:
+                    if j not in self.backend_connectivity_diagram.get(i, []):
+                        non_executable_interactions.append((i, j))
+
+        if non_executable_interactions:
+            error_message = (
+                f"The following qubit interactions in the circuit prevent a 1-to-1 mapping:"
+                f"{set(non_executable_interactions)}"
+            )
+            raise ValueError(error_message)

test/router/test_routing_checker.py

@@ -0,0 +1,52 @@
+# Tests for routing checker pass
+
+import pytest
+
+from opensquirrel import CircuitBuilder
+from opensquirrel.circuit import Circuit
+from opensquirrel.passes.router.routing_checker import RoutingChecker
+
+
+@pytest.fixture(name="router")
+def router_fixture() -> RoutingChecker:
+    backend_connectivity_diagram = {0: [1, 2], 1: [0, 2, 3], 2: [0, 1, 4], 3: [1, 4], 4: [2, 3]}
+    return RoutingChecker(backend_connectivity_diagram)
+
+
+@pytest.fixture
+def circuit1() -> Circuit:
+    builder = CircuitBuilder(5)
+    builder.H(0)
+    builder.CNOT(0, 1)
+    builder.H(2)
+    builder.CNOT(1, 2)
+    builder.CNOT(2, 4)
+    builder.CNOT(3, 4)
+    return builder.to_circuit()
+
+
+@pytest.fixture
+def circuit2() -> Circuit:
+    builder = CircuitBuilder(5)
+    builder.H(0)
+    builder.CNOT(0, 1)
+    builder.CNOT(0, 3)
+    builder.H(2)
+    builder.CNOT(1, 2)
+    builder.CNOT(1, 3)
+    builder.CNOT(2, 3)
+    builder.CNOT(3, 4)
+    builder.CNOT(0, 4)
+    return builder.to_circuit()
+
+
+def test_routing_checker_possible_1to1_mapping(router: RoutingChecker, circuit1: Circuit) -> None:
+    try:
+        router.route(circuit1.ir)
+    except ValueError:
+        pytest.fail("route() raised ValueError unexpectedly")
+
+
+def test_routing_checker_impossible_1to1_mapping(router: RoutingChecker, circuit2: Circuit) -> None:
+    with pytest.raises(ValueError, match="The following qubit interactions in the circuit prevent a 1-to-1 mapping:.*"):
+        router.route(circuit2.ir)

test/test_integration.py

@@ -16,6 +16,7 @@
 )
 from opensquirrel.passes.exporter import ExportFormat
 from opensquirrel.passes.merger.single_qubit_gates_merger import SingleQubitGatesMerger
+from opensquirrel.passes.router.routing_checker import RoutingChecker
 
 
 def test_spin_backend() -> None:
@@ -44,6 +45,10 @@ def test_spin_backend() -> None:
         """,
     )
 
+    # Check whether the above algorithm can be mapped to a dummy chip topology
+    connectivity = {0: [1, 2], 1: [0], 2: [0, 3], 3: [2]}
+
+    qc.route(router=RoutingChecker(connectivity))
     # Decompose 2-qubit gates to a decomposition where the 2-qubit interactions are captured by CNOT gates
     qc.decompose(decomposer=CNOTDecomposer())