Add support for Python example (CMake) (openxla#2113)

This is the canonical Python example similar to what was recently
introduced for C++ in openxla#2083

* Add a stablehlo_add.py file which demonstrates nice usage of the
Python bindings API
* Integrate it with the CMake build system
* Introduce a CMakePresets for buildings and Python bindings

We have never had support for building Python bindings with Bazel so
that support is missing as of this PR as well.

```console
❯ cmake --build --preset debug-python --target stablehlo-python-add
[89/89] cd /usr/local/google/home/fmzakari/code/github.com/open...ages/stablehlo /tmp/stablehlo-venv/bin/python3 stablehlo_add.py
module {
  func.func @main() -> tensor<3x4xi64> {
    %0 = stablehlo.constant dense<0> : tensor<3x4xi64>
    %1 = stablehlo.constant dense<0> : tensor<3x4xi64>
    %2 = stablehlo.add %0, %1 : tensor<3x4xi64>
    return %2 : tensor<3x4xi64>
  }
}
```

CMakePresets.json

@@ -19,6 +19,27 @@
             "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
             "MLIR_DIR": "${sourceDir}/llvm-build/lib/cmake/mlir"
           }
+        },
+        {
+          "name": "debug-python",
+          "displayName": "Debug w/ python bindings",
+          "inherits": "debug",
+          "cacheVariables": {
+            "STABLEHLO_ENABLE_BINDINGS_PYTHON" : "ON",
+            "STABLEHLO_ENABLE_SANITIZER": "OFF"
+          }
+        }
+      ],
+      "buildPresets": [
+        {
+          "name": "debug",
+          "displayName": "Build Debug",
+          "configurePreset": "debug"
+        },
+        {
+          "name": "debug-python",
+          "displayName": "Build Debug w/ python bindings",
+          "configurePreset": "debug-python"
         }
     ]
 }

examples/CMakeLists.txt

@@ -1,4 +1,4 @@
-# Copyright 2024 The TensorFlow Authors. All Rights Reserved.
+# Copyright 2024 The StableHLO Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -13,3 +13,7 @@
 # limitations under the License.
 
 add_subdirectory(c++)
+
+if(STABLEHLO_ENABLE_BINDINGS_PYTHON)
+  add_subdirectory(python)
+endif()

examples/python/CMakeLists.txt

@@ -0,0 +1,15 @@
+# Copyright 2024 The StableHLO Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+add_stablehlo_python_test(stablehlo-python-add stablehlo_add.py)

examples/python/README.md

@@ -0,0 +1,9 @@
+# Python Examples
+
+This directory should contain a series of examples as a starting point
+for how to use StableHLO via our Python bindings.
+
+Note: If you have a great example to highlight, we welcome contributions!
+
+* [stablehlo_add](./stablehlo_add.py): A simple example that demonstrates
+how to use the StableHLO library to add two numbers.

examples/python/stablehlo_add.py

@@ -0,0 +1,37 @@
+# Copyright 2024 The StableHLO Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from mlir import ir
+import mlir.dialects.stablehlo as stablehlo
+import mlir.dialects.func as func
+from mlir.ir import Context, Location, InsertionPoint, Module
+import numpy as np
+
+with Context() as ctx, Location.unknown():
+  stablehlo.register_dialect(ctx)
+  module = Module.create()
+
+  with InsertionPoint(module.body):
+
+    @func.func()
+    def main():
+      a_value = ir.DenseElementsAttr.get(np.zeros(shape=[3,4], dtype=np.int64))
+      b_value = ir.DenseElementsAttr.get(np.zeros(shape=[3,4], dtype=np.int64))
+      a = stablehlo.constant(a_value)
+      b = stablehlo.constant(b_value)
+      add = stablehlo.add(a, b)
+      return add
+
+assert main.func_op.verify()
+print(str(module))