✨ Implement Trials For Mapping Pass (#1568)

Author: MatthiasReumann

CHANGELOG.md

@@ -13,7 +13,7 @@ This project adheres to [Semantic Versioning], with the exception that minor rel
 
 - ✨ Add Sampler and Estimator Primitives to the QDMI-Qiskit Interface ([#1507]) ([**@marcelwa**])
 - ✨ Add conversions between Jeff and QCO ([#1479], [#1548]) ([**@denialhaag**])
-- ✨ Add a `place-and-route` pass for mapping circuits to architectures with restricted topologies ([#1537], [#1547]) ([**@MatthiasReumann**])
+- ✨ Add a `place-and-route` pass for mapping circuits to architectures with restricted topologies ([#1537], [#1547], [#1568]) ([**@MatthiasReumann**])
 - ✨ 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], [#1548], [#1550], [#1554])
   ([**@burgholzer**], [**@denialhaag**], [**@taminob**], [**@DRovara**], [**@li-mingbao**], [**@Ectras**], [**@MatthiasReumann**], [**@simon1hofmann**])
@@ -331,6 +331,7 @@ _📚 Refer to the [GitHub Release Notes](https://github.com/munich-quantum-tool
 
 <!-- PR links -->
 
+[#1568]: https://github.com/munich-quantum-toolkit/core/pull/1568
 [#1554]: https://github.com/munich-quantum-toolkit/core/pull/1554
 [#1550]: https://github.com/munich-quantum-toolkit/core/pull/1550
 [#1549]: https://github.com/munich-quantum-toolkit/core/pull/1549

mlir/include/mlir/Dialect/QCO/Transforms/Mapping/Architecture.h

@@ -64,6 +64,12 @@ class [[nodiscard]] Architecture {
   [[nodiscard]] mlir::SmallVector<std::size_t, 4>
   neighboursOf(std::size_t u) const;
 
+  /**
+   * @brief Return the maximum degree (connectivity) of any qubit in the
+   * architecture.
+   */
+  [[nodiscard]] std::size_t maxDegree() const;
+
 private:
   using Matrix = mlir::SmallVector<mlir::SmallVector<std::size_t, 0>, 0>;
 

mlir/include/mlir/Dialect/QCO/Transforms/Passes.td

@@ -49,6 +49,9 @@ def MappingPass : Pass<"place-and-route", "mlir::ModuleOp"> {
     each traversal, the pass routes the circuit and updates the dynamic-to-static mapping based on the routing decisions
     made during that traversal. By performing multiple traversals, the pass can iteratively refine the mapping and
     potentially find a more optimal solution. This is behavior is controlled by the `niterations` parameter.
+
+    The pass option `ntrials` determines how many random initial layouts the pass explores. Per default, the pass always
+    explores the identity layout. If compiled with multi-threading on, these trials will be executed in parallel.
   }];
   let options = [
     Option<"nlookahead", "nlookahead", "std::size_t", "1",
@@ -58,7 +61,11 @@ def MappingPass : Pass<"place-and-route", "mlir::ModuleOp"> {
     Option<"lambda", "lambda", "float", "0.5F",
            "The lambda factor in the cost function.">,
     Option<"niterations", "niterations", "std::size_t", "2",
-           "The number of forwards and backwards traversal to improve the initial layout.">
+           "The number of forwards and backwards traversal to improve the initial layout.">,
+    Option<"ntrials", "ntrials", "std::size_t", "4",
+           "The number of (possibly parallel) random trials of the forwards and backwards mechanism.">,
+    Option<"seed", "seed", "std::size_t", "42",
+           "A seed used for randomization.">
   ];
 }
 

mlir/lib/Dialect/QCO/Transforms/Mapping/Architecture.cpp

@@ -13,6 +13,7 @@
 #include <llvm/Support/ErrorHandling.h>
 #include <mlir/Support/LLVM.h>
 
+#include <algorithm>
 #include <cstddef>
 #include <cstdint>
 #include <string_view>
@@ -72,3 +73,11 @@ void Architecture::collectNeighbours() {
     neighbours_[u].push_back(v);
   }
 }
+
+std::size_t Architecture::maxDegree() const {
+  std::size_t deg = 0;
+  for (const auto& nbrs : neighbours_) {
+    deg = std::max(deg, nbrs.size());
+  }
+  return deg;
+}