[iOS] Disable NNPACK on iOS builds (#39868)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39868

### Summary

why disable NNPACK on iOS

- To stay consistency with our internal version
- It's currently blocking some external users due to its lack support of x86 architecture
    - https://github.com/pytorch/pytorch/issues/32040
    - https://discuss.pytorch.org/t/undefined-symbols-for-architecture-x86-64-for-libtorch-in-swift-unit-test/84552/6
- NNPACK uses fast convolution algorithms (FFT, winograd) to reduce the computational complexity of convolutions with large kernel size. The algorithmic speedup is limited to specific conv params which are unlikely to appear in mobile networks.
- Since XNNPACK has been enabled, it performs much better than NNPACK on depthwise-separable convolutions which is the algorithm being used by most of mobile computer vision networks.

### Test Plan

- CI Checks

Test Plan: Imported from OSS

Differential Revision: D22087365

Pulled By: xta0

fbshipit-source-id: 89a959b0736c1f8703eff10723a8fbd02357fd4a

.circleci/scripts/binary_ios_upload.sh

@@ -22,8 +22,6 @@ do
         lipo -create "${libs[@]}" -o ${ZIP_DIR}/install/lib/${lib}
     fi
 done
-# for nnpack, we only support arm64 build
-cp ${ARTIFACTS_DIR}/arm64/lib/libnnpack.a ./
 lipo -i ${ZIP_DIR}/install/lib/*.a
 # copy the umbrella header and license
 cp ${PROJ_ROOT}/ios/LibTorch.h ${ZIP_DIR}/src/

ios/TestApp/benchmark/setup.rb

@@ -63,7 +63,7 @@ targets.each do |target|
     target.resources_build_phase.add_file_reference(config_file_ref, true)
 end
 puts "Linking static libraries..."
-libs = ['libc10.a', 'libclog.a', 'libnnpack.a', 'libXNNPACK.a', 'libeigen_blas.a', 'libcpuinfo.a', 'libpytorch_qnnpack.a', 'libtorch_cpu.a', 'libtorch.a']
+libs = ['libc10.a', 'libclog.a', 'libXNNPACK.a', 'libeigen_blas.a', 'libcpuinfo.a', 'libpytorch_qnnpack.a', 'libtorch_cpu.a', 'libtorch.a']
 targets.each do |target|
     target.frameworks_build_phases.clear
     for lib in libs do

scripts/build_ios.sh

@@ -62,11 +62,8 @@ fi
 
 # IOS_PLATFORM controls type of iOS platform (see ios-cmake)
 if [ -n "${IOS_PLATFORM:-}" ]; then
-  CMAKE_ARGS+=("-DIOS_PLATFORM=${IOS_PLATFORM}")
-  if [ "${IOS_PLATFORM}" == "SIMULATOR" ]; then
-      # iOS Simulator build is not supported by NNPACK
-      CMAKE_ARGS+=("-DUSE_NNPACK=OFF")
-  elif [ "${IOS_PLATFORM}" == "WATCHOS" ]; then
+  CMAKE_ARGS+=("-DIOS_PLATFORM=${IOS_PLATFORM}")    
+  if [ "${IOS_PLATFORM}" == "WATCHOS" ]; then
       # enable bitcode by default for watchos
       CMAKE_ARGS+=("-DCMAKE_C_FLAGS=-fembed-bitcode")
       CMAKE_ARGS+=("-DCMAKE_CXX_FLAGS=-fembed-bitcode")
@@ -95,6 +92,7 @@ CMAKE_ARGS+=("-DUSE_LMDB=OFF")
 CMAKE_ARGS+=("-DUSE_LEVELDB=OFF")
 CMAKE_ARGS+=("-DUSE_MPI=OFF")
 CMAKE_ARGS+=("-DUSE_NUMPY=OFF")
+CMAKE_ARGS+=("-DUSE_NNPACK=OFF")
 
 # pthreads
 CMAKE_ARGS+=("-DCMAKE_THREAD_LIBS_INIT=-lpthread")

scripts/xcode_build.rb

@@ -51,7 +51,7 @@ end
 
 # link static libraries
 target.frameworks_build_phases.clear
-libs = ['libc10.a', 'libclog.a', 'libnnpack.a', 'libXNNPACK.a', 'libeigen_blas.a', 'libcpuinfo.a', 'libpytorch_qnnpack.a', 'libtorch_cpu.a', 'libtorch.a']
+libs = ['libc10.a', 'libclog.a', 'libXNNPACK.a', 'libeigen_blas.a', 'libcpuinfo.a', 'libpytorch_qnnpack.a', 'libtorch_cpu.a', 'libtorch.a']
 for lib in libs do
     path = "#{install_path}/lib/#{lib}"
     if File.exist?(path)