'Peephole' optimization - or: collecting and optimizing two-qubit blocks - before routing

qiskit/transpiler/passes/optimization/split_2q_unitaries.py

@@ -68,6 +68,9 @@ def run(self, dag: DAGCircuit):
                 decomp._inner_decomposition.specialization
                 == TwoQubitWeylDecomposition._specializations.SWAPEquiv
             ):
-                # TODO also look at swap-gate-like gates?
+                # TODO maybe also look into swap-gate-like gates? Things to consider:
+                #   * As the qubit mapping may change, we'll always need to build a new dag in this pass
+                #   * There may not be many swap-gate-like gates in an arbitrary input circuit
+                #   * Removing swap gates from a user-routed input circuit here is unexpected
                 pass
         return dag

qiskit/transpiler/preset_passmanagers/builtin_plugins.py

@@ -73,7 +73,15 @@
 
 CONFIG = user_config.get_config()
 
-_discrete_skipped_ops = {"delay", "reset", "measure"}
+_discrete_skipped_ops = {
+    "delay",
+    "reset",
+    "measure",
+    "switch_case",
+    "if_else",
+    "for_loop",
+    "while_loop",
+}
 
 
 class DefaultInitPassManager(PassManagerStagePlugin):
@@ -181,11 +189,10 @@ def _is_one_op_non_discrete(ops):
                     if isinstance(op, str):
                         op = stdgates.get(op, None)
 
-                    if (
-                        op is None
-                        or not isinstance(op, Instruction)
-                        or op.name in _discrete_skipped_ops
-                    ):
+                    if op is None or not isinstance(op, Instruction):
+                        return False
+
+                    if op.name in _discrete_skipped_ops:
                         continue
 
                     if len(op.params) > 0:
@@ -207,7 +214,7 @@ def _is_one_op_non_discrete(ops):
             if do_consolidate_blocks_init:
                 init.append(Collect2qBlocks())
                 init.append(ConsolidateBlocks())
-                init.append(Split2QUnitaries())
+                init.append(Split2QUnitaries(pass_manager_config.approximation_degree))
         else:
             raise TranspilerError(f"Invalid optimization level {optimization_level}")
         return init