I'm currently pondering an IR format for a mildly optimizing C23 implementation, and am curious how C11 atomic operations would look like in sea-of-nodes. The representation seems to be completely opposite to the programming model, where strict ordering and memory fencing are required. libFirm[0] is probably the most sophisticated sea-of-nodes based AOT compilers I'm aware of, it's a shame they ceased development before implementing atomics.

[0] https://pp.ipd.kit.edu/firm/Features.html