Fix MLIR Python binding for arith.constant after argument has been changed to an interface

[mehdi_amini]

Summary

e1795322844c removed the Type field from attributes and
arith::ConstantOp argument is now a TypedAttrInterface which isn't
supported by the python generator.
This patch temporarily restore the functionality for arith.constant but
won't generalize: we need to work on the generator instead.

[ftynse]

mlir/python/mlir/dialects/_arith_ops_ext.py

64

Nit: the code above and below seems to be fine without the builtins. namespace.

mlir/test/python/dialects/arith_dialect.py

17

Nit: it's okay to construct constants directly in the module, we don't need this extra complexity in the test.

[mehdi_amini]

Address comments

mlir/python/mlir/dialects/_arith_ops_ext.py

 #  Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 #  See https://llvm.org/LICENSE.txt for license information.
 #  SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 try:
   from ..ir import *
   from ._ods_common import get_default_loc_context as _get_default_loc_context
 
   from typing import Any, List, Union
+  import builtins
 except ImportError as e:
   raise RuntimeError("Error loading imports from extension module") from e
 
 
 def _isa(obj: Any, cls: type):
   try:
     cls(obj)
   except ValueError:
return cls(
         value,
         loc=loc,
         ip=ip)
 
   @property
   def type(self):
     return self.results[0].type
 
+  @builtins.property
+  def value(self):
+    return Attribute(self.operation.attributes["value"])
+
   @property
   def literal_value(self) -> Union[int, float]:
     if _is_integer_like_type(self.type):
       return IntegerAttr(self.value).value
     elif _is_float_type(self.type):
       return FloatAttr(self.value).value
     else:
       raise ValueError("only integer and float constants have literal values")

mlir/test/python/dialects/arith_dialect.py

+# RUN: %PYTHON %s | FileCheck %s
+
+from mlir.ir import *
+import mlir.dialects.func as func
+import mlir.dialects.arith as arith
+
+def run(f):
+  print("\nTEST:", f.__name__)
+  f()
+
+# CHECK-LABEL: TEST: testConstantOp
+@run
+def testConstantOps():
+  with Context() as ctx, Location.unknown():
+    module = Module.create()
+    with InsertionPoint(module.body):
+      @func.FuncOp.from_py_func()
+      def emit_constant_float():
+        return arith.ConstantOp(value=42.42, result=F32Type.get())
+
+    # CHECK-LABEL: func @emit_constant_float
+    # CHECK:         %cst = arith.constant 4.242000e+01 : f32
+    # CHECK:         return
+    # CHECK:       }
+    print(module)