Now that I could agree with, the only place where hiccups have started to occur are with wave intrinsics where you can share data between thread in a wave without halting execution. I'm not sure disallowing it would be the best idea as it cuts out possible optimizations, but outright allowing it without the user knowing the number of lanes can cause it's own problems. My job is the fun time of fixing issues in other peoples code related to all of this. I have no stakes in rust though, I'd rather write a custom spirv compiler.