Support qasm construction from QObj

Signed-off-by: Thien Nguyen <nguyentm@ornl.gov>

quantum/plugins/ibm/accelerator/IBMAccelerator.cpp

@@ -1260,7 +1260,30 @@ IBMAccelerator::getNativeCode(std::shared_ptr<CompositeInstruction> program,
     return jsonStr;
   } else if (format == "qasm" || format == "Qasm" || format == "QASM" ||
              format == "OpenQASM" || format == "OPENQASM") {
-    return "";
+    chosenBackend = availableBackends[backend];
+    const auto basis_gates =
+        chosenBackend["basis_gates"].get<std::vector<std::string>>();
+    // If the gate set has "u3" -> old gateset.
+    const auto gateSet = (xacc::container::contains(basis_gates, "u3"))
+                             ? QObjectExperimentVisitor::GateSet::U_CX
+                             : QObjectExperimentVisitor::GateSet::RZ_SX_CX;
+    auto visitor = std::make_shared<QObjectExperimentVisitor>(
+        program->name(), program->nLogicalBits(), gateSet);
+    InstructionIterator it(program);
+    int memSlots = 0;
+    while (it.hasNext()) {
+      auto nextInst = it.next();
+      if (nextInst->isEnabled()) {
+        nextInst->accept(visitor);
+      }
+    }
+    auto experiment = visitor->getExperiment();
+    std::stringstream ss;
+    for (auto &inst : experiment.get_instructions()) {
+      // std::cout << "HOWDY: " << inst.toString() << "\n";
+      ss << inst.toString() << "\n";
+    }
+    return ss.str();
   }
   xacc::error("Unknown native code format '" + format + "'");
   return "";

quantum/plugins/ibm/accelerator/json/QObject.hpp

@@ -399,6 +399,26 @@ public:
 
   std::optional<int64_t> get_condition_reg_id() const { return conditional; }
   void set_condition_reg_id(int64_t value) { this->conditional = value; }
+
+  std::string toString() const {
+    std::stringstream ss;
+    ss << name;
+    if (!params.empty()) {
+      ss << "(";
+      for (int i = 0; i < params.size(); ++i) {
+        ss << params[i];
+        if (i != params.size() - 1) {
+          ss << ", ";
+        }
+      }
+      ss << ")";
+    }
+    for (const auto &qb : qubits) {
+      ss << " q[" << qb << "]";
+    }
+    ss << ";";
+    return ss.str();
+  }
 };
 
 class Experiment {