🐛 Fix dangling references in collectQubitValuesInsideSCFOps

CHANGELOG.md

@@ -18,7 +18,7 @@ This project adheres to [Semantic Versioning], with the exception that minor rel
 - ✨ Add conversions between `jeff` and QCO ([#1479], [#1548], [#1565], [#1637], [#1676], [#1706]) ([**@denialhaag**], [**@burgholzer**])
 - ✨ Add a `place-and-route` pass for mapping circuits to architectures with restricted topologies ([#1537], [#1547], [#1568], [#1581], [#1583], [#1588], [#1600], [#1664], [#1709], [#1716], [#1748]) ([**@MatthiasReumann**], [**@burgholzer**])
 - ✨ Add initial infrastructure for new QC and QCO MLIR dialects
-  ([#1264], [#1330], [#1402], [#1428], [#1430], [#1436], [#1443], [#1446], [#1464], [#1465], [#1470], [#1471], [#1472], [#1474], [#1475], [#1506], [#1510], [#1513], [#1521], [#1542], [#1548], [#1550], [#1554], [#1567], [#1569], [#1570], [#1572], [#1573], [#1580], [#1602], [#1620], [#1623], [#1624], [#1626], [#1627], [#1635], [#1638], [#1673], [#1675], [#1700], [#1717], [#1728], [#1730])
+  ([#1264], [#1330], [#1402], [#1428], [#1430], [#1436], [#1443], [#1446], [#1464], [#1465], [#1470], [#1471], [#1472], [#1474], [#1475], [#1506], [#1510], [#1513], [#1521], [#1542], [#1548], [#1550], [#1554], [#1567], [#1569], [#1570], [#1572], [#1573], [#1580], [#1602], [#1620], [#1623], [#1624], [#1626], [#1627], [#1635], [#1638], [#1673], [#1675], [#1700], [#1717], [#1728], [#1730], [#1749])
   ([**@burgholzer**], [**@denialhaag**], [**@taminob**], [**@DRovara**], [**@li-mingbao**], [**@Ectras**], [**@MatthiasReumann**], [**@simon1hofmann**])
 
 ### Changed
@@ -402,6 +402,7 @@ _📚 Refer to the [GitHub Release Notes](https://github.com/munich-quantum-tool
 
 <!-- PR links -->
 
+[#1749]: https://github.com/munich-quantum-toolkit/core/pull/1749
 [#1748]: https://github.com/munich-quantum-toolkit/core/pull/1748
 [#1737]: https://github.com/munich-quantum-toolkit/core/pull/1737
 [#1730]: https://github.com/munich-quantum-toolkit/core/pull/1730

mlir/lib/Conversion/QCToQCO/QCToQCO.cpp

@@ -515,13 +515,7 @@ static void extractQubitsAfterOp(LoweringState& state, Operation* target,
  */
 static std::pair<SetVector<Value>, SetVector<Value>>
 collectQubitValuesInsideSCFOps(Operation* op, LoweringState* state) {
-  // Get the regions of the current operation
-  const auto& regions = op->getRegions();
-  auto& regionQubitMap = state->regionQubitMap[op];
-  auto& regionRegisterMap = state->regionRegisterMap[op];
-
-  for (auto& region : regions) {
-    auto& qubitInfoMap = state->qubitInfoMap[&region];
+  for (auto& region : op->getRegions()) {
     // Skip empty regions e.g. empty else region of an If operation
     if (region.empty()) {
       continue;
@@ -534,12 +528,16 @@ collectQubitValuesInsideSCFOps(Operation* op, LoweringState* state) {
       if (operation.getNumRegions() > 0) {
         auto [qubits, registers] =
             collectQubitValuesInsideSCFOps(&operation, state);
+        auto& regionQubitMap = state->regionQubitMap[op];
+        auto& qubitInfoMap = state->qubitInfoMap[&region];
         regionQubitMap.set_union(qubits);
         // Remove duplicate qubits
         regionQubitMap.remove_if(
             [&](Value qubit) { return qubitInfoMap.contains(qubit); });
-        regionRegisterMap.set_union(registers);
+        state->regionRegisterMap[op].set_union(registers);
       }
+      auto& qubitInfoMap = state->qubitInfoMap[&region];
+      auto& regionRegisterMap = state->regionRegisterMap[op];
       // Track qubits from loadOp
       if (auto loadOp = dyn_cast<memref::LoadOp>(operation)) {
         QubitInfo info{.reg = loadOp.getMemRef(),
@@ -548,6 +546,7 @@ collectQubitValuesInsideSCFOps(Operation* op, LoweringState* state) {
         regionRegisterMap.insert(loadOp.getMemRef());
         continue;
       }
+      auto& regionQubitMap = state->regionQubitMap[op];
       // Add the QC qubit and memref operands to the maps
       for (const auto& operand : operation.getOperands()) {
         if (isa<qc::QubitType>(operand.getType())) {
@@ -564,7 +563,7 @@ collectQubitValuesInsideSCFOps(Operation* op, LoweringState* state) {
     }
   }
 
-  return {regionQubitMap, regionRegisterMap};
+  return {state->regionQubitMap[op], state->regionRegisterMap[op]};
 }
 
 namespace {

mlir/unittests/Conversion/QCOToQC/test_qco_to_qc.cpp

@@ -527,10 +527,13 @@ INSTANTIATE_TEST_SUITE_P(
                     QCOToQCTestCase{"SingleControlledX",
                                     MQT_NAMED_BUILDER(qco::singleControlledX),
                                     MQT_NAMED_BUILDER(qc::singleControlledX)},
+                    QCOToQCTestCase{"MultipleControlledX",
+                                    MQT_NAMED_BUILDER(qco::multipleControlledX),
+                                    MQT_NAMED_BUILDER(qc::multipleControlledX)},
                     QCOToQCTestCase{
-                        "MultipleControlledX",
-                        MQT_NAMED_BUILDER(qco::multipleControlledX),
-                        MQT_NAMED_BUILDER(qc::multipleControlledX)}));
+                        "RepeatedControlledX",
+                        MQT_NAMED_BUILDER(qco::repeatedControlledX),
+                        MQT_NAMED_BUILDER(qc::repeatedControlledX)}));
 /// @}
 
 /// \name QCOToQC/Operations/StandardGates/XxMinusYyOp.cpp

mlir/unittests/Conversion/QCToQCO/test_qc_to_qco.cpp

@@ -525,15 +525,19 @@ INSTANTIATE_TEST_SUITE_P(
 /// @{
 INSTANTIATE_TEST_SUITE_P(
     QCXOpTest, QCToQCOTest,
-    testing::Values(QCToQCOTestCase{"X", MQT_NAMED_BUILDER(qc::x),
-                                    MQT_NAMED_BUILDER(qco::x)},
-                    QCToQCOTestCase{"SingleControlledX",
-                                    MQT_NAMED_BUILDER(qc::singleControlledX),
-                                    MQT_NAMED_BUILDER(qco::singleControlledX)},
-                    QCToQCOTestCase{
-                        "MultipleControlledX",
+    testing::Values(
+        QCToQCOTestCase{"X", MQT_NAMED_BUILDER(qc::x),
+                        MQT_NAMED_BUILDER(qco::x)},
+        QCToQCOTestCase{"SingleControlledX",
+                        MQT_NAMED_BUILDER(qc::singleControlledX),
+                        MQT_NAMED_BUILDER(qco::singleControlledX)},
+        QCToQCOTestCase{"MultipleControlledX",
                         MQT_NAMED_BUILDER(qc::multipleControlledX),
-                        MQT_NAMED_BUILDER(qco::multipleControlledX)}));
+                        MQT_NAMED_BUILDER(qco::multipleControlledX)},
+        QCToQCOTestCase{"RepeatedControlledX",
+                        MQT_NAMED_BUILDER(qc::repeatedControlledX),
+                        MQT_NAMED_BUILDER(qco::repeatedControlledX)}));
+
 /// @}
 
 /// \name QCToQCO/Operations/StandardGates/XxMinusYyOp.cpp

mlir/unittests/programs/qc_programs.cpp

@@ -271,6 +271,15 @@ void trivialControlledX(QCProgramBuilder& b) {
   b.mcx({}, q[0]);
 }
 
+void repeatedControlledX(QCProgramBuilder& b) {
+  auto control = b.allocQubit();
+  b.h(control);
+  for (auto i = 0; i < 50; i++) {
+    auto qubit = b.allocQubit();
+    b.cx(control, qubit);
+  }
+}
+
 void inverseX(QCProgramBuilder& b) {
   auto q = b.allocQubitRegister(1);
   b.inv([&]() { b.x(q[0]); });

mlir/unittests/programs/qc_programs.h

@@ -171,6 +171,9 @@ void nestedControlledX(QCProgramBuilder& b);
 /// Creates a circuit with a trivial controlled X gate.
 void trivialControlledX(QCProgramBuilder& b);
 
+/// Creates a circuit with repeated controlled X gates.
+void repeatedControlledX(QCProgramBuilder& b);
+
 /// Creates a circuit with an inverse modifier applied to an X gate.
 void inverseX(QCProgramBuilder& b);
 

mlir/unittests/programs/qco_programs.cpp

@@ -271,6 +271,15 @@ void trivialControlledX(QCOProgramBuilder& b) {
   b.mcx({}, q[0]);
 }
 
+void repeatedControlledX(QCOProgramBuilder& b) {
+  auto q0 = b.allocQubit();
+  auto control = b.h(q0);
+  for (auto i = 0; i < 50; i++) {
+    auto qubit = b.allocQubit();
+    control = b.cx(control, qubit).first;
+  }
+}
+
 void inverseX(QCOProgramBuilder& b) {
   auto q = b.allocQubitRegister(1);
   b.inv({q[0]}, [&](ValueRange qubits) { return SmallVector{b.x(qubits[0])}; });

mlir/unittests/programs/qco_programs.h

@@ -158,6 +158,9 @@ void nestedControlledX(QCOProgramBuilder& b);
 /// Creates a circuit with a trivial controlled X gate.
 void trivialControlledX(QCOProgramBuilder& b);
 
+/// Creates a circuit with repeated controlled X gates.
+void repeatedControlledX(QCOProgramBuilder& b);
+
 /// Creates a circuit with an inverse modifier applied to an X gate.
 void inverseX(QCOProgramBuilder& b);