Assuming no compiler bugs, no. UB isn't something "caused" by optimizations, it's something that exists in the code before optimizations, optimizations can jus

Assuming no compiler bugs, no. UB isn't something "caused" by optimizations, it's something that exists in the code before optimizations, optimizations can just trigger nasal demons. So you shouldn't be able to write UB in safe Rust assuming no compiler bugs. (And assuming that any unsafe libraries being leveraged are bug free)