the clang compiler does not support '-march=armv8.2-a+bf16' when build xnnpack for android

[feifeicoder]

Follow the tutorial to build xnnpack runtime lib for android with NDK r19 and meet such errors:

[ 91%] Building C object backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-1x4c8-minmax-neonbf16-bfmlal.c.o
[ 91%] Building C object backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-1x4c8-minmax-neonbf16-bfdot.c.o
[ 91%] Building C object backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-1x8c2-minmax-neonbf16-bfdot-lane-ld128.c.o
clang: error: the clang compiler does not support '-march=armv8.2-a+bf16'
gmake[2]: *** [backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/build.make:43241: backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-1x4c8-minmax-neonbf16-bfmlal.c.o] Error 1

[agunapal]

Getting the same error

[ 92%] Building C object backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-1x4c8-minmax-neonbf16-bfdot.c.o
[ 92%] Building C object backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-2x4c8-minmax-neonbf16-bfmlal.c.o
[ 92%] Building C object backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-1x4c8-minmax-neonbf16-bfmlal.c.o
[ 92%] Building C object backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-2x4c8-minmax-neonbf16-bfdot.c.o
[ 92%] Building C object backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-1x8c2-minmax-neonbf16-bfdot-lane-ld128.c.o
clang: error: the clang compiler does not support '-march=armv8.2-a+bf16'
make[2]: *** [backends/xnnpack/third-party/XNNPACK/CMakeFiles/microkernels-all.dir/src/bf16-gemm/gen/bf16-gemm-2x4c8-minmax-neonbf16-bfmlal.c.o] Error 1
make[2]: *** Waiting for unfinished jobs....
clang: error: the clang compiler does not support '-march=armv8.2-a+bf16'

[metascroy]

@digantdesai do you know a work around for this issue with clang?

[metascroy]

It looks like a similar issue was filed in XNNPACK and the suggested solution was to disable bf16 with -DXNNPACK_ENABLE_ARM_BF16=OFF (google/XNNPACK#3618). I guess using GCC might also work, but maybe there's a better option with clang

[agunapal]

Thanks! That works

[digantdesai]

Thanks @metascroy for the suggestion.

Yeah I guess the right way would be to check (by tracking minimum_supported_version for clang in this case) if the compiler supports, this and enable only when it does. AndXNNPACK_ENABLE_ARM_BF16=OFF is just a static version of that.

That said BF16 was enabled by LLVM a while ago (2020?), and is the reason to enable by default.