[MLIR][python bindings] Add TypeCaster for returning refined types from python APIs

depends on D150839

This diff uses `MlirTypeID` to register `TypeCaster`s (i.e., `[](PyType pyType) -> DerivedTy { return pyType; }`) for all concrete types (i.e., `PyConcrete<...>`) that are then queried for (by `MlirTypeID`) and called in `struct type_caster<MlirType>::cast`. The result is that anywhere an `MlirType mlirType` is returned from a python binding, that `mlirType` is automatically cast to the correct concrete type. For example:

```
      c0 = arith.ConstantOp(f32, 0.0)
      # CHECK: F32Type(f32)
      print(repr(c0.result.type))

      unranked_tensor_type = UnrankedTensorType.get(f32)
      unranked_tensor = tensor.FromElementsOp(unranked_tensor_type, [c0]).result

      # CHECK: UnrankedTensorType
      print(type(unranked_tensor.type).__name__)
      # CHECK: UnrankedTensorType(tensor<*xf32>)
      print(repr(unranked_tensor.type))
```

This functionality immediately extends to typed attributes (i.e., `attr.type`).

The diff also implements similar functionality for `mlir_type_subclass`es but in a slightly different way - for such types (which have no cpp corresponding `class` or `struct`) the user must provide a type caster in python (similar to how `AttrBuilder` works) or in cpp as a `py::cpp_function`.

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D150927

1 files changed, 11 insertions, 6 deletions

diff --git a/mlir/lib/Bindings/Python/IRModule.h b/mlir/lib/Bindings/Python/IRModule.h
index cfa3737..013bb7b 100644
--- a/mlir/lib/Bindings/Python/IRModule.h
+++ b/mlir/lib/Bindings/Python/IRModule.h
@@ -13,6 +13,7 @@
 #include <utility>
 #include <vector>
 
+#include "Globals.h"
 #include "PybindUtils.h"
 
 #include "mlir-c/AffineExpr.h"
@@ -868,9 +869,7 @@ public:
 
   PyConcreteType() = default;
   PyConcreteType(PyMlirContextRef contextRef, MlirType t)
-      : BaseTy(std::move(contextRef), t) {
-    pybind11::implicitly_convertible<PyType, DerivedTy>();
-  }
+      : BaseTy(std::move(contextRef), t) {}
   PyConcreteType(PyType &orig)
       : PyConcreteType(orig.getContext(), castFrom(orig)) {}
 
@@ -914,6 +913,13 @@ public:
       return printAccum.join();
     });
 
+    if (DerivedTy::getTypeIdFunction) {
+      PyGlobals::get().registerTypeCaster(
+          DerivedTy::getTypeIdFunction(),
+          pybind11::cpp_function(
+              [](PyType pyType) -> DerivedTy { return pyType; }));
+    }
+
     DerivedTy::bindDerived(cls);
   }
 
@@ -1009,9 +1015,8 @@ public:
           return DerivedTy::isaFunction(otherAttr);
         },
         pybind11::arg("other"));
-    cls.def_property_readonly("type", [](PyAttribute &attr) {
-      return PyType(attr.getContext(), mlirAttributeGetType(attr));
-    });
+    cls.def_property_readonly(
+        "type", [](PyAttribute &attr) { return mlirAttributeGetType(attr); });
     DerivedTy::bindDerived(cls);
   }