Update on "Remove ExecuTorch copy of Vectorized"

All uses are outside ExecuTorch core, so we can just use ATen Vectorized.

Differential Revision: [D66396016](https://our.internmc.facebook.com/intern/diff/D66396016/)

[ghstack-poisoned]

Author: swolchok

.ci/scripts/build_llama_android.sh

@@ -15,7 +15,6 @@ if [[ -z "${PYTHON_EXECUTABLE:-}" ]]; then
 fi
 which "${PYTHON_EXECUTABLE}"
 CMAKE_PREFIX_PATH="$(python3 -c 'import torch as _; print(_.__path__[0])')"
-SITE_PACKAGES="$(${PYTHON_EXECUTABLE} -c 'from distutils.sysconfig import get_python_lib; print(get_python_lib())')"
 
 install_executorch_and_backend_lib() {
   echo "Installing executorch and xnnpack backend"
@@ -29,7 +28,6 @@ install_executorch_and_backend_lib() {
     -DANDROID_ABI="${ANDROID_ABI}" \
     -DCMAKE_INSTALL_PREFIX=cmake-android-out \
     -DCMAKE_BUILD_TYPE=Release \
-    -DCMAKE_FIND_ROOT_PATH="${SITE_PACKAGES}" \
     -DCMAKE_PREFIX_PATH="${CMAKE_PREFIX_PATH}" \
     -DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=ON \
     -DEXECUTORCH_BUILD_EXTENSION_MODULE=ON \

build/build_android_llm_demo.sh

@@ -40,10 +40,8 @@ build_android_native_library() {
   else
     EXECUTORCH_BUILD_NEURON=OFF
   fi
-  SITE_PACKAGES="$(${PYTHON_EXECUTABLE} -c 'from distutils.sysconfig import get_python_lib; print(get_python_lib())')"
 
   cmake . -DCMAKE_INSTALL_PREFIX="${CMAKE_OUT}" \
-    -DCMAKE_FIND_ROOT_PATH="${SITE_PACKAGES}" \
     -DCMAKE_PREFIX_PATH="${CMAKE_PREFIX_PATH}" \
     -DCMAKE_TOOLCHAIN_FILE="${ANDROID_NDK}/build/cmake/android.toolchain.cmake" \
     -DANDROID_ABI="${ANDROID_ABI}" \
@@ -78,7 +76,6 @@ build_android_native_library() {
     -DANDROID_ABI="${ANDROID_ABI}" \
     -DANDROID_PLATFORM=android-26 \
     -DCMAKE_INSTALL_PREFIX="${CMAKE_OUT}" \
-    -DCMAKE_FIND_ROOT_PATH="${SITE_PACKAGES}" \
     -DCMAKE_PREFIX_PATH="${CMAKE_PREFIX_PATH}" \
     -DEXECUTORCH_ENABLE_LOGGING=ON \
     -DEXECUTORCH_LOG_LEVEL=Info \

extension/llm/custom_ops/CMakeLists.txt

@@ -68,8 +68,9 @@ target_compile_options(
 install(TARGETS custom_ops DESTINATION lib)
 
 if(EXECUTORCH_BUILD_KERNELS_CUSTOM_AOT)
-  # Add a AOT library
-  find_package(Torch CONFIG REQUIRED)
+  # Use NO_CMAKE_FIND_ROOT_PATH to make sure this works even if
+  # cross-compiling. See note in kernels/optimized/CMakeLists.txt.
+  find_package(Torch CONFIG REQUIRED NO_CMAKE_FIND_ROOT_PATH)
   add_library(
     custom_ops_aot_lib SHARED
     ${_custom_ops__srcs}

kernels/optimized/CMakeLists.txt

@@ -63,7 +63,14 @@ message("Generated files ${gen_command_sources}")
 
 list(TRANSFORM _optimized_kernels__srcs PREPEND "${EXECUTORCH_ROOT}/")
 add_library(optimized_kernels ${_optimized_kernels__srcs})
-find_package(Torch CONFIG REQUIRED)
+# We require Torch headers, which setup.py puts in CMAKE_PREFIX_PATH
+# for us. Toolchains that we might be using for cross-compiling could
+# set CMAKE_FIND_ROOT_PATH, which prevents find_package from finding
+# headers not rooted under CMAKE_FIND_ROOT_PATH. This is reasonable
+# for binary dependencies because they probably aren't built for the
+# target platform, but for our header-only use case, we should just
+# ignore CMAKE_FIND_ROOT_PATH.
+find_package(Torch CONFIG REQUIRED NO_CMAKE_FIND_ROOT_PATH)
 target_include_directories(optimized_kernels PRIVATE ${TORCH_INCLUDE_DIRS})
 target_link_libraries(
   optimized_kernels PRIVATE executorch_core cpublas extension_threadpool