Python bindings: support __floordiv__ for index types

The original reimplementation of EDSC as declarative builders and the
    subsequent rework of Python bindings forbade to use the (true) division
    operator for values of the index types without providing an alternative.  Index
    types only support floor and ceil division through affine maps.  Expose this to
    Python bindings through a `__floordiv__` function on `ValueHandle`s.

--

PiperOrigin-RevId: 241713093

mlir/bindings/python/pybind.cpp

@@ -1234,6 +1234,9 @@ PYBIND11_MODULE(pybind, m) {
         .def("__truediv__",
              [](PythonValueHandle lhs, PythonValueHandle rhs)
                  -> PythonValueHandle { return lhs.value / rhs.value; })
+        .def("__floordiv__",
+             [](PythonValueHandle lhs, PythonValueHandle rhs)
+                 -> PythonValueHandle { return floorDiv(lhs, rhs); })
         .def("__mod__",
              [](PythonValueHandle lhs, PythonValueHandle rhs)
                  -> PythonValueHandle { return lhs.value % rhs.value; })

mlir/bindings/python/test/test_py2and3.py

@@ -308,6 +308,18 @@ class EdscTest(unittest.TestCase):
     self.assertIn("%true_2 = constant 1 : i1", code)
     self.assertIn("%8 = subi %true_2, %7 : i1", code)
 
+  def testDivisions(self):
+    with self.module.function_context(
+        "division", [self.indexType, self.i32Type, self.i32Type], []) as fun:
+      # indices only support floor division
+      fun.arg(0) // E.constant_index(42)
+      # regular values only support regular division
+      fun.arg(1) / fun.arg(2)
+
+    code = str(self.module)
+    self.assertIn("floordiv 42", code)
+    self.assertIn("divis %arg1, %arg2 : i32", code)
+
   def testCustom(self):
     with self.module.function_context("custom", [self.indexType, self.f32Type],
                                       []) as fun: