[mlir][python] Include anchor op in PassManager constructor

[rkayaith]

Summary

This adds an extra argument for specifying the pass manager's anchor op,
with a default of any. Previously the anchor was always defaulted to
builtin.module.

[rkayaith]

update summary

[rkayaith]

rebase

mlir/lib/Bindings/Python/Pass.cpp

 } // namespace
 
 /// Create the `mlir.passmanager` here.
 void mlir::python::populatePassManagerSubmodule(py::module &m) {
   //----------------------------------------------------------------------------
   // Mapping of the top-level PassManager
   //----------------------------------------------------------------------------
   py::class_<PyPassManager>(m, "PassManager", py::module_local())
-      .def(py::init<>([](DefaultingPyMlirContext context) {
+      .def(py::init<>([](const std::string &anchorOp,
+                         DefaultingPyMlirContext context) {
              MlirPassManager passManager = mlirPassManagerCreate(
                  context->get(),
-                 mlirStringRefCreateFromCString("builtin.module"));
+                 mlirStringRefCreate(anchorOp.data(), anchorOp.size()));
              return new PyPassManager(passManager);
            }),
+           py::arg("anchor_op") = py::str("any"),
            py::arg("context") = py::none(),
            "Create a new PassManager for the current (or provided) Context.")
       .def_property_readonly(MLIR_PYTHON_CAPI_PTR_ATTR,
                              &PyPassManager::getCapsule)
       .def(MLIR_PYTHON_CAPI_FACTORY_ATTR, &PyPassManager::createFromCapsule)
       .def("_testing_release", &PyPassManager::release,
            "Releases (leaks) the backing pass manager (testing)")
       .def(

mlir/test/python/pass_manager.py

with Context():
     pm = PassManager()
     pm_capsule = pm._CAPIPtr
     assert '"mlir.passmanager.PassManager._CAPIPtr"' in repr(pm_capsule)
     pm._testing_release()
     pm1 = PassManager._CAPICreate(pm_capsule)
     assert pm1 is not None  # And does not crash.
 run(testCapsule)
 
+# CHECK-LABEL: TEST: testConstruct
+@run
+def testConstruct():
+  with Context():
+    # CHECK: pm1: 'any()'
+    # CHECK: pm2: 'builtin.module()'
+    pm1 = PassManager()
+    pm2 = PassManager("builtin.module")
+    log(f"pm1: '{pm1}'")
+    log(f"pm2: '{pm2}'")
+
 
 # Verify successful round-trip.
 # CHECK-LABEL: TEST: testParseSuccess
 def testParseSuccess():
   with Context():
     # An unregistered pass should not parse.
     try:
       pm = PassManager.parse("builtin.module(func.func(not-existing-pass{json=false}))")