WIP: only build the targets we need

Author: dbort

setup.py

@@ -323,8 +323,10 @@ def initialize_options(self):
         # setuptools/_distutils/command/build.py for the default.
         self.build_base = "pip-out"
 
-        # Default to 9 jobs, but allow overriding through the environment.
-        self.parallel = os.environ.get("CMAKE_BUILD_PARALLEL_LEVEL", "9")
+        # Default build parallelism based on number of cores, but allow
+        # overriding through the environment.
+        default_parallel = str(os.cpu_count() - 1)
+        self.parallel = os.environ.get("CMAKE_BUILD_PARALLEL_LEVEL", default_parallel)
 
     def run(self):
         self.dump_options()
@@ -352,20 +354,28 @@ def run(self):
             f"-DCMAKE_BUILD_TYPE={cfg}",
         ]
 
-        # TODO(dbort): This block should also assemble the list of targets to
-        # build so we only build what we need.
+        build_args = [f"-j{self.parallel}"]
+
+        # TODO(dbort): Try to manage these targets and the cmake args from the
+        # extension entries themselves instead of hard-coding them here.
+        build_args += ["--target", "flatc"]
+
         if ShouldBuild.aot_util:
             cmake_args += [
                 "-DEXECUTORCH_BUILD_EXTENSION_AOT_UTIL=ON",
             ]
+            build_args += ["--target", "aot_util"]
         if ShouldBuild.pybindings:
             cmake_args += [
                 "-DEXECUTORCH_BUILD_PYBIND=ON",
             ]
+            build_args += ["--target", "portable_lib"]
             if ShouldBuild.xnnpack:
                 cmake_args += [
                     "-DEXECUTORCH_BUILD_XNNPACK=ON",
                 ]
+                # No target needed; the cmake arg will link xnnpack
+                # into the portable_lib target.
             # TODO(dbort): Add MPS/CoreML backends when building on macos.
 
         # Allow adding extra cmake args through the environment. Used by some
@@ -374,8 +384,6 @@ def run(self):
         if "CMAKE_ARGS" in os.environ:
             cmake_args += [item for item in os.environ["CMAKE_ARGS"].split(" ") if item]
 
-        build_args = [f"-j{self.parallel}"]
-
         # Put the cmake cache under the temp directory, like
         # "pip-out/temp.<plat>/cmake-out".
         cmake_cache_dir = os.path.join(repo_root, self.build_temp, "cmake-out")