torchao setup.py with cmake (#1490)

Summary:

Initial draft of using cmake in torchao's build process.

Install torchao with:

```
USE_CPP=1 pip install .
```

If on an arm64 machine, it builds the dynamic library for torchao at site-packages/torchao/libtorchao_ops_aten.dylib.  On import of torchao, if this library is found it is loaded.

Reviewed By: kimishpatel, drisspg

Differential Revision: D67777662

Author: metascroy

setup.py

@@ -8,7 +8,7 @@
 import subprocess
 from datetime import datetime
 
-from setuptools import find_packages, setup
+from setuptools import Extension, find_packages, setup
 
 current_date = datetime.now().strftime("%Y%m%d")
 
@@ -41,6 +41,14 @@ def read_version(file_path="version.txt"):
 
 use_cpp = os.getenv("USE_CPP")
 
+import platform
+
+build_torchao_experimental = (
+    use_cpp == "1"
+    and platform.machine().startswith("arm64")
+    and platform.system() == "Darwin"
+)
+
 version_prefix = read_version()
 # Version is version.dev year month date if using nightlies and version if not
 version = (
@@ -49,6 +57,11 @@ def read_version(file_path="version.txt"):
     else version_prefix
 )
 
+
+def use_debug_mode():
+    return os.getenv("DEBUG", "0") == "1"
+
+
 import torch
 from torch.utils.cpp_extension import (
     CUDA_HOME,
@@ -59,8 +72,61 @@ def read_version(file_path="version.txt"):
 )
 
 
+# BuildExtension is a subclass of from setuptools.command.build_ext.build_ext
+class TorchAOBuildExt(BuildExtension):
+    def __init__(self, *args, **kwargs) -> None:
+        super().__init__(*args, **kwargs)
+
+    def build_extensions(self):
+        cmake_extensions = [
+            ext for ext in self.extensions if isinstance(ext, CMakeExtension)
+        ]
+        other_extensions = [
+            ext for ext in self.extensions if not isinstance(ext, CMakeExtension)
+        ]
+        for ext in cmake_extensions:
+            self.build_cmake(ext)
+
+        # Use BuildExtension to build other extensions
+        self.extensions = other_extensions
+        super().build_extensions()
+
+        self.extensions = other_extensions + cmake_extensions
+
+    def build_cmake(self, ext):
+        extdir = os.path.abspath(os.path.dirname(self.get_ext_fullpath(ext.name)))
+
+        build_type = "Debug" if use_debug_mode() else "Release"
+
+        from distutils.sysconfig import get_python_lib
+
+        torch_dir = get_python_lib() + "/torch/share/cmake/Torch"
+
+        if not os.path.exists(self.build_temp):
+            os.makedirs(self.build_temp)
+
+        subprocess.check_call(
+            [
+                "cmake",
+                ext.sourcedir,
+                "-DCMAKE_BUILD_TYPE=" + build_type,
+                "-DTORCHAO_BUILD_EXECUTORCH_OPS=OFF",
+                "-DTorch_DIR=" + torch_dir,
+                "-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=" + extdir,
+            ],
+            cwd=self.build_temp,
+        )
+        subprocess.check_call(["cmake", "--build", "."], cwd=self.build_temp)
+
+
+class CMakeExtension(Extension):
+    def __init__(self, name, sourcedir=""):
+        Extension.__init__(self, name, sources=[])
+        self.sourcedir = os.path.abspath(sourcedir)
+
+
 def get_extensions():
-    debug_mode = os.getenv("DEBUG", "0") == "1"
+    debug_mode = use_debug_mode()
     if debug_mode:
         print("Compiling in debug mode")
 
@@ -129,18 +195,25 @@ def get_extensions():
     if use_cuda:
         sources += cuda_sources
 
-    if len(sources) == 0:
-        return None
+    ext_modules = []
+    if len(sources) > 0:
+        ext_modules.append(
+            extension(
+                "torchao._C",
+                sources,
+                py_limited_api=True,
+                extra_compile_args=extra_compile_args,
+                extra_link_args=extra_link_args,
+            )
+        )
 
-    ext_modules = [
-        extension(
-            "torchao._C",
-            sources,
-            py_limited_api=True,
-            extra_compile_args=extra_compile_args,
-            extra_link_args=extra_link_args,
+    if build_torchao_experimental:
+        ext_modules.append(
+            CMakeExtension(
+                "torchao.experimental",
+                sourcedir="torchao/experimental",
+            )
         )
-    ]
 
     return ext_modules
 
@@ -159,6 +232,6 @@ def get_extensions():
     long_description=open("README.md").read(),
     long_description_content_type="text/markdown",
     url="https://github.com/pytorch/ao",
-    cmdclass={"build_ext": BuildExtension},
+    cmdclass={"build_ext": TorchAOBuildExt},
     options={"bdist_wheel": {"py_limited_api": "cp39"}},
 )

torchao/__init__.py

@@ -32,6 +32,18 @@
         assert len(so_files) == 1, f"Expected one _C*.so file, found {len(so_files)}"
         torch.ops.load_library(so_files[0])
         from . import ops
+
+        # The following library contains CPU kernels from torchao/experimental
+        # They are built automatically by ao/setup.py if on an ARM machine.
+        # They can also be built outside of the torchao install process by
+        # running the script `torchao/experimental/build_torchao_ops.sh <aten|executorch>`
+        # For more information, see https://github.com/pytorch/ao/blob/main/torchao/experimental/docs/readme.md
+        experimental_lib = list(Path(__file__).parent.glob("libtorchao_ops_aten.*"))
+        if len(experimental_lib) > 0:
+            assert (
+                len(experimental_lib) == 1
+            ), f"Expected at most one libtorchao_ops_aten.* file, found {len(experimental_lib)}"
+            torch.ops.load_library(experimental_lib[0])
     except:
         logging.debug("Skipping import of cpp extensions")