✨ Add a pass hoisting auxiliary qubits out of callees

CHANGELOG.md

@@ -64,7 +64,7 @@ releases may include breaking changes.
 #### Passes and transformations
 
 - ✨ Add passes for quantum-specific interprocedural optimizations ([#2193],
-  [#2197], [#2198]) ([**@DRovara**], [**@burgholzer**])
+  [#2197], [#2198], [#2199]) ([**@DRovara**], [**@burgholzer**])
 - ✨ Add Pauli twirling, quantum loop unrolling, and qubit reuse passes
   ([#1705], [#1718], [#1755], [#1756], [#1923], [#1924], [#2039], [#2118],
   [#2216], [#2224]) ([**@MatthiasReumann**], [**@DRovara**], [**@burgholzer**],
@@ -890,6 +890,7 @@ for previous changelogs._
 [#2216]: https://github.com/munich-quantum-toolkit/core/pull/2216
 [#2203]: https://github.com/munich-quantum-toolkit/core/pull/2203
 [#2214]: https://github.com/munich-quantum-toolkit/core/pull/2214
+[#2199]: https://github.com/munich-quantum-toolkit/core/pull/2199
 [#2198]: https://github.com/munich-quantum-toolkit/core/pull/2198
 [#2197]: https://github.com/munich-quantum-toolkit/core/pull/2197
 [#2196]: https://github.com/munich-quantum-toolkit/core/pull/2196

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

@@ -370,6 +370,26 @@ def QuantumArgumentPromotion
                            "mlir::qco::QCODialect"];
 }
 
+def AuxiliaryQubitHoisting
+    : Pass<"quantum-auxiliary-qubit-hoisting", "mlir::ModuleOp"> {
+  let summary = "Turn callee-internal qubits into arguments";
+  let description = [{
+        A qubit that a callee allocates and releases itself becomes an extra
+        argument, and its release point becomes a `qco.reset` handed back as an
+        extra result. The caller then owns the allocation and can reuse one
+        qubit across several calls.
+
+        Externally visible functions, declarations, recursive functions, and
+        functions with more than one block are left alone, as are allocations
+        nested inside a region.
+    }];
+
+  let dependentDialects = ["::mlir::func::FuncDialect",
+                           "::mlir::arith::ArithDialect",
+                           "::mlir::qtensor::QTensorDialect",
+                           "mlir::qco::QCODialect"];
+}
+
 def RemoveDeadGates : Pass<"remove-dead-gates", "mlir::ModuleOp"> {
   let dependentDialects = ["mlir::qco::QCODialect"];
   let summary = "Remove quantum gates whose results cannot be observed";