[clang] [llvm] [BPF] Make -mcpu=v3 as the default (PR #107008)

[via llvm-commits]

yonghong-song wrote:

Thanks @yuvald-sweet-security I am not sure whether I can add default v1->v3 in llvm20 or not. But let me check anyway.

Also, if the verification failure can be easily reproduced, could you submit the test case, we can do some analysis to see why and maybe verifier could be improved due to this. Thanks!

https://github.com/llvm/llvm-project/pull/107008