Yeah that’s a common optimization for poll checks. I think most production JVMs do that.

I’m very far from doing those kinds of low level optimizations because I have a large pile of very high level and very basic optimizations still left to do!

We did it for MaxineVM back in the day, having the thread-local-storage point to itself and the safepoint as a load back into the same register. The problem is that that introduces a chain of dependent loads for all safepoints and for all operations that use thread-local storage. That seems like it would hurt OOE and IPC as a result.

I am working on adding threads to Virgil (slowly, in the background, heh). I'll use the simple load+branch from the TLS for the simple reason that the GC code is also written in Virgil and it must be possible to turn off safepoints that have been inserted into the GC code itself, which is easy and robust to do if they are thread-local.