On Tue, Dec 1, 2020 at 4:38 AM Brendan Jackman <jackm...@google.com> wrote: > > I guess it's also worth remembering other archs might have an atomic > subtract.
which one? arm64 LSE implements atomic_fetch_sub as neg+ldadd. imo x64 and arm64 example outweighs choices by other archs if there are such. Even without LSE it will be neg+llsc loop. The reason I proposed bpf xsub insn earlier is that I thought that llvm won't be able to emit it so easily and JIT/verifier would struggle.
