[MLIR][Python] fix PyRegionList __iter__

mlir/lib/Bindings/Python/IRCore.cpp

@@ -204,8 +204,8 @@ namespace {
 
 class PyRegionIterator {
 public:
-  PyRegionIterator(PyOperationRef operation)
-      : operation(std::move(operation)) {}
+  PyRegionIterator(PyOperationRef operation, int nextIndex)
+      : operation(std::move(operation)), nextIndex(nextIndex) {}
 
   PyRegionIterator &dunderIter() { return *this; }
 
@@ -228,7 +228,7 @@ class PyRegionIterator {
 
 private:
   PyOperationRef operation;
-  int nextIndex = 0;
+  intptr_t nextIndex = 0;
 };
 
 /// Regions of an op are fixed length and indexed numerically so are represented
@@ -247,7 +247,7 @@ class PyRegionList : public Sliceable<PyRegionList, PyRegion> {
 
   PyRegionIterator dunderIter() {
     operation->checkValid();
-    return PyRegionIterator(operation);
+    return PyRegionIterator(operation, startIndex);
   }
 
   static void bindDerived(ClassTy &c) {

mlir/lib/Bindings/Python/NanobindUtils.h

@@ -395,7 +395,6 @@ class Sliceable {
   /// Hook for derived classes willing to bind more methods.
   static void bindDerived(ClassTy &) {}
 
-private:
   intptr_t startIndex;
   intptr_t length;
   intptr_t step;

mlir/test/python/ir/operation.py

@@ -2,12 +2,12 @@
 
 import gc
 import io
-import itertools
 from tempfile import NamedTemporaryFile
 from mlir.ir import *
 from mlir.dialects.builtin import ModuleOp
-from mlir.dialects import arith
+from mlir.dialects import arith, func, scf
 from mlir.dialects._ods_common import _cext
+from mlir.extras import types as T
 
 
 def run(f):
@@ -1199,3 +1199,27 @@ def testGetOwnerConcreteOpview():
             r = arith.AddIOp(a, a, overflowFlags=arith.IntegerOverflowFlags.nsw)
             for u in a.result.uses:
                 assert isinstance(u.owner, arith.AddIOp)
+
+
+# CHECK-LABEL: TEST: testIndexSwitch
+@run
+def testIndexSwitch():
+    with Context() as ctx, Location.unknown():
+        i32 = T.i32()
+        module = Module.create()
+        with InsertionPoint(module.body):
+
+            @func.FuncOp.from_py_func(T.index())
+            def index_switch(index):
+                c1 = arith.constant(i32, 1)
+                switch_op = scf.IndexSwitchOp(
+                    results_=[i32], arg=index, cases=range(3), num_caseRegions=3
+                )
+
+                assert len(switch_op.regions) == 4
+                assert len(switch_op.regions[2:]) == 2
+                assert len([i for i in switch_op.regions[2:]]) == 2
+                assert len(switch_op.caseRegions) == 3
+                assert len([i for i in switch_op.caseRegions]) == 3
+                assert len(switch_op.caseRegions[1:]) == 2
+                assert len([i for i in switch_op.caseRegions[1:]]) == 2