On Wed, 2023-11-08 at 21:30 -0800, Yonghong Song wrote: > With latest llvm18 (main branch of llvm-project repo), when building bpf selftests, > [~/work/bpf-next (master)]$ make -C tools/testing/selftests/bpf LLVM=1 -j > > The following compilation error happens: > fatal error: error in backend: Branch target out of insn range > ... > Stack dump: > 0. Program arguments: clang -g -Wall -Werror -D__TARGET_ARCH_x86 -mlittle-endian > -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/include > -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf -I/home/yhs/work/bpf-next/tools/include/uapi > -I/home/yhs/work/bpf-next/tools/testing/selftests/usr/include -idirafter > /home/yhs/work/llvm-project/llvm/build.18/install/lib/clang/18/include -idirafter /usr/local/include > -idirafter /usr/include -Wno-compare-distinct-pointer-types -DENABLE_ATOMICS_TESTS -O2 --target=bpf > -c progs/pyperf180.c -mcpu=v3 -o /home/yhs/work/bpf-next/tools/testing/selftests/bpf/pyperf180.bpf.o > 1. <eof> parser at end of file > 2. Code generation > ... > > The compilation failure only happens to cpu=v2 and cpu=v3. cpu=v4 is okay > since cpu=v4 supports 32-bit branch target offset. > > The above failure is due to upstream llvm patch [1] where some inlining behavior > are changed in llvm18. > > To workaround the issue, previously all 180 loop iterations are fully unrolled. > Now, the fully unrolling count is changed to 90 for llvm18 and later. This reduced > some otherwise long branch target distance, and fixed the compilation failure. > > [1] https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e > > Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx> Can confirm, the issue is present on clang main w/o this patch and disappears after this patch. Yonghong, is there a way to keep original UNROLL_COUNT if cpuv4 is used? Tested-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
