Add MergeCircuitMeasuresPass and RemoveUnusedCircuitsPass (openqasm#255)

Adds a MergeCircuitMeasuresPass to merge quir.measures inside
circuits. Based on `MergeMeasuresTopologicalPass`.

Adds a RemoveUnusedCircuitsPass to clean up unused circuits and reduce the number of operations in a module.

include/Dialect/QUIR/Transforms/MergeCircuitMeasures.h

@@ -0,0 +1,42 @@
+//===- MergeCircuitMeasures.h - Merge measurement ops in circuits - C++ -*-===//
+//
+// (C) Copyright IBM 2024.
+//
+// This code is part of Qiskit.
+//
+// This code is licensed under the Apache License, Version 2.0 with LLVM
+// Exceptions. You may obtain a copy of this license in the LICENSE.txt
+// file in the root directory of this source tree.
+//
+// Any modifications or derivative works of this code must retain this
+// copyright notice, and modified files need to carry a notice indicating
+// that they have been altered from the originals.
+//
+//===----------------------------------------------------------------------===//
+///
+///  This file declares the pass for merging measurements inside circuits into a
+///  single measure op
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef QUIR_MERGE_CIRCUIT_MEASURES_H
+#define QUIR_MERGE_CIRCUIT_MEASURES_H
+
+#include "mlir/Pass/Pass.h"
+
+namespace mlir::quir {
+
+/// @brief Merge together measures in a circuit that are topologically
+/// adjacent into a single variadic measurement.
+struct MergeCircuitMeasuresTopologicalPass
+    : public PassWrapper<MergeCircuitMeasuresTopologicalPass, OperationPass<>> {
+  void runOnOperation() override;
+
+  llvm::StringRef getArgument() const override;
+  llvm::StringRef getDescription() const override;
+  llvm::StringRef getName() const override;
+}; // struct MergeCircuitMeasuresTopologicalPass
+
+} // namespace mlir::quir
+
+#endif // QUIR_MERGE_CIRCUIT_MEASURES_H

include/Dialect/QUIR/Transforms/Passes.h

@@ -23,11 +23,13 @@
 #include "ConvertDurationUnits.h"
 #include "FunctionArgumentSpecialization.h"
 #include "LoadElimination.h"
+#include "MergeCircuitMeasures.h"
 #include "MergeCircuits.h"
 #include "MergeMeasures.h"
 #include "MergeParallelResets.h"
 #include "QuantumDecoration.h"
 #include "RemoveQubitOperands.h"
+#include "RemoveUnusedCircuits.h"
 #include "ReorderCircuits.h"
 #include "ReorderMeasurements.h"
 #include "SubroutineCloning.h"

include/Dialect/QUIR/Transforms/RemoveUnusedCircuits.h

@@ -0,0 +1,41 @@
+//===- RemoveUnusedCircuits.h - Remove Unused Circuits  ----------- C++ -*-===//
+//
+// (C) Copyright IBM 2024.
+//
+// This code is part of Qiskit.
+//
+// This code is licensed under the Apache License, Version 2.0 with LLVM
+// Exceptions. You may obtain a copy of this license in the LICENSE.txt
+// file in the root directory of this source tree.
+//
+// Any modifications or derivative works of this code must retain this
+// copyright notice, and modified files need to carry a notice indicating
+// that they have been altered from the originals.
+//
+//===----------------------------------------------------------------------===//
+///
+///  This file declares the pass for removing unused circuits.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef QUIR_REMOVE_UNUSED_CIRCUITS_H
+#define QUIR_REMOVE_UNUSED_CIRCUITS_H
+
+#include "mlir/Pass/Pass.h"
+
+namespace mlir::quir {
+
+/// @brief Merge together measures in a circuit that are topologically
+/// adjacent into a single variadic measurement.
+struct RemoveUnusedCircuitsPass
+    : public PassWrapper<RemoveUnusedCircuitsPass, OperationPass<>> {
+  void runOnOperation() override;
+
+  llvm::StringRef getArgument() const override;
+  llvm::StringRef getDescription() const override;
+  llvm::StringRef getName() const override;
+}; // struct RemoveUnusedCircuits
+
+} // namespace mlir::quir
+
+#endif // QUIR_REMOVE_UNUSED_CIRCUITS_H

lib/Dialect/QUIR/Transforms/CMakeLists.txt

@@ -19,12 +19,14 @@ add_mlir_dialect_library(MLIRQUIRTransforms
     FunctionArgumentSpecialization.cpp
     LoadElimination.cpp
     MergeCircuits.cpp
+    MergeCircuitMeasures.cpp
     MergeMeasures.cpp
     MergeParallelResets.cpp
     Passes.cpp
     QuantumDecoration.cpp
     QUIRCircuitAnalysis.cpp
     RemoveQubitOperands.cpp
+    RemoveUnusedCircuits.cpp
     ReorderMeasurements.cpp
     ReorderCircuits.cpp
     SubroutineCloning.cpp