There are a few rare cases where compiler optimization will fail this in GCC. There are also cases where the C spec has defined behavior that optimizers break.

There are a few rare cases where compiler optimization will fail this in GCC. There are also cases where the C spec has defined behavior that optimizers break. Where I know about them, I file bugs. It would be up for users to insist that those get fixed. This includes optimization issues that affect Rust as well.