Merge pull request #202 from BQSKit/pam-barrier-fix

Pam barrier fix

Author: edyounis

bqskit/passes/mapping/pam.py

@@ -13,6 +13,7 @@
 import numpy as np
 
 from bqskit.ir.circuit import Circuit
+from bqskit.ir.gates.barrier import BarrierPlaceholder
 from bqskit.ir.gates.constant.swap import SwapGate
 from bqskit.ir.point import CircuitPoint
 from bqskit.passes.mapping.sabre import GeneralizedSabreAlgorithm
@@ -175,6 +176,13 @@ def forward_pass(  # type: ignore
                 E = self._calc_extended_set(circuit, F)
                 for n in execute_list:
                     op = circuit[n]
+
+                    if isinstance(op.gate, BarrierPlaceholder):
+                        if modify_circuit:
+                            physical_location = [pi[q] for q in op.location]
+                            mapped_circuit.append_gate(op.gate, op.location)
+                        continue
+
                     p1, circ, p2 = self._get_best_perm(
                         circuit,
                         perm_data[n],

bqskit/passes/mapping/sabre.py

@@ -9,6 +9,7 @@
 import numpy as np
 
 from bqskit.ir.circuit import Circuit
+from bqskit.ir.gates.barrier import BarrierPlaceholder
 from bqskit.ir.gates.circuitgate import CircuitGate
 from bqskit.ir.gates.constant.swap import SwapGate
 from bqskit.ir.operation import Operation
@@ -330,6 +331,9 @@ def backward_pass(
 
     def _can_exe(self, op: Operation, pi: list[int], cg: CouplingGraph) -> bool:
         """Return true if `op` is executable given the current mapping `pi`."""
+        if isinstance(op.gate, BarrierPlaceholder):
+            return True
+
         if isinstance(op.gate, CircuitGate):
             if all(g.num_qudits == 1 for g in op.gate._circuit.gate_set):
                 return True